Exhibit 99.1

SUPPLEMENTAL FEDERAL INCOME TAX CONSIDERATIONS

This discussion is a supplement to, and is intended to be read together with, the discussion under the heading “Federal Income Tax Considerations” in the Registration Statement on Form S-3 (File No. 333-177052) of CoreSite Realty Corporation (the “Company”) filed with the Securities and Exchange Commission on September 28, 2011 (the “2011 Registration Statement) and in the related prospectus dated October 11, 2011 (the “Base Prospectus”) of the Company and the discussion under the heading “Federal Income Tax Considerations” in the Registration Statement on Form S-3 (File No. 333-198951) of the Company filed with the Securities and Exchange Commission on September 26, 2014 (the “2014 Registration Statement”).

The following discussion is inserted at the beginning of the discussion under the heading “Federal Income Tax Considerations—Taxation of Our Company” in the Base Prospectus and at the beginning of the discussion under the heading “Federal Income Tax Considerations—Taxation of Our Company” in the 2014 Registration Statement.

The following information is generally applicable to and modifies the discussion below:

·                   Although we have received private letter rulings from the IRS on certain matters, we have not requested and do not intend to request a ruling from the IRS that we qualify as a REIT, and the statements in this prospectus are not binding on the IRS or any court. We are entitled to rely upon our private letter rulings only to the extent that we did not misstate or omit a material fact in the ruling requests we submitted to the IRS and that we operate in the future in accordance with the facts described in those requests.

·                   We currently hold interests in more than one taxable REIT subsidiary.

The following discussion supersedes the first sentence of the ninth bullet point in the fourth paragraph in the discussion under the heading “Federal Income Tax Considerations—Taxation of Our Company—General” in the Base Prospectus.

Ninth, if we acquire any asset from a corporation that is or has been a C corporation in a transaction in which our initial basis in the asset is less than the fair market value of the asset at the time we acquire the asset, and we subsequently recognize gain on the disposition of the asset during the ten-year period beginning on the date on which we acquired the asset, then we will be required to pay tax at the highest regular corporate tax rate on this gain to the extent of the excess of (1) the fair market value of the asset over (2) our adjusted basis in the asset, in each case determined as of the date on which we acquired the asset.

The following discussion is inserted as a new bullet point after the twelfth bullet point in the fourth paragraph in the discussion under the heading “Federal Income Tax Considerations—Taxation of Our Company—General” in the Base Prospectus.

Thirteenth, if we fail to comply with the requirement to send annual letters to our stockholders requesting information regarding the actual ownership of our stock and the failure is not due to reasonable cause or due to willful neglect, we will be subject to a $25,000 penalty, or if the failure is intentional, a $50,000 penalty.

The following discussion supersedes the first paragraph in the discussion under the heading “Federal Income Tax Considerations—Taxation of Our Company—Tax Aspects of Our Operating Partnership, the Subsidiary Partnerships and the Limited Liability Companies—Allocations of Income, Gain, Loss and Deduction” in the Base Prospectus.

The net income and loss of our operating partnership are allocated in accordance with the terms of the partnership agreement. In general, the net income and net loss of our operating partnership are allocated to the holders of partnership units in such a manner that, to the extent possible, the capital account of each holder, as adjusted in accordance with certain applicable Treasury Regulations, is equal to the amount that would be distributed to such holder in a hypothetical liquidation of the operating partnership. Therefore, as a result of the preference to which the preferred partnership units are entitled in distributions, net income may be disproportionately allocated to the holders of preferred partnership units, including us, and net loss may be disproportionately allocated to the holders of common partnership units. In some cases losses may also be disproportionately allocated to partners who have guaranteed debt of our operating partnership.

The following discussion supersedes the discussion under the heading “Federal Income Tax Considerations—Federal Income Tax Considerations for Holders of Our Common Stock—Taxation of Non-U.S. Stockholders—Foreign Accounts” in the Base Prospectus.

Withholding taxes may be imposed under Sections 1471 through 1474 of the Code (commonly referred to as the Foreign Account Tax Compliance Act, or FATCA) on certain types of payments made to non-U.S. financial institutions and certain other non-U.S. entities. Specifically, a 30% withholding tax may be imposed on dividends on, or gross proceeds from the sale or other disposition of, our capital stock paid to a “foreign financial institution” or a “non-financial foreign entity” (each as defined in the Code), unless (1) in the case of a foreign financial institution, the foreign financial institution undertakes certain diligence and reporting obligations, (2) in the case of a non-financial foreign entity, the non-financial foreign entity either certifies it does not have any “substantial United States owners” (as defined in the Code) or furnishes identifying information regarding each substantial United States owner or (3) the foreign financial institution or non-financial foreign entity otherwise qualifies for an exemption from these rules. If the payee is a foreign financial institution and is subject to the diligence and reporting requirements referred to in clause (1) above, it must enter into an agreement with the U.S. Department of the Treasury requiring, among other things, that it undertake to identify accounts held by certain “specified United States persons” or “United States-owned foreign entities” (each as defined in the Code), annually report certain information about such accounts and withhold 30% on certain payments to non-compliant foreign financial institutions and certain other account holders. Non-U.S. entities located in jurisdictions that have an intergovernmental agreement with the United States governing FATCA may be subject to different rules. Under the applicable Treasury Regulations, withholding under FATCA generally applies to payments of dividends on our capital stock regardless of when they are made and will apply to payments of gross proceeds from the sale or other disposition of our capital stock on or after January 1, 2017. Prospective investors should consult their tax advisors regarding these rules.

Exhibit 99.2

SUPPLEMENT TO DESCRIPTION OF SECURITIES

This discussion is a supplement to, and is intended to be read together with, the discussion under the heading “Description of Securities” in the Registration Statement on Form S-3 (File No. 333-177052) of CoreSite Realty Corporation (the “Company”) filed with the Securities and Exchange Commission on September 28, 2011 (the “Registration Statement) and in the related prospectus dated October 11, 2011 (the “Base Prospectus”) of the Company. This discussion is not complete and is subject to, and qualified in its entirety by reference to, Maryland law and the Company’s charter and bylaws, which are available as described under “Where You Can Find More Information” in the Base Prospectus.

The following discussion is inserted immediately before the subheading “Description of Securities—Power to Increase Authorized Stock and Issue Additional Shares of Our Common Stock and Preferred Stock” in the Base Prospectus.

7.25% Series A Cumulative Redeemable Preferred Stock

We currently have outstanding 4,600,000 shares of our 7.25% Series A Cumulative Redeemable Preferred Stock, $0.01 par value per share, or Series A Preferred Stock. Our Series A Preferred Stock is listed on the NYSE under the symbol “COR-PA.” Dividends on each outstanding share of Series A Preferred Stock are cumulative from, and including, the most recent dividend payment date for the Series A Preferred Stock with respect to which dividends were actually paid in full on the outstanding shares of Series A Preferred Stock, or if dividends have not been paid in full on the outstanding shares of Series A Preferred Stock from December 12, 2012, the original date of issuance of the Series A Preferred Stock. Dividends are payable in cash to holders quarterly in arrears on or about the 15th day of January, April, July and October of each year or, if such day is not a business day, on the next succeeding business day.

If our company is liquidated, dissolved or wound up, holders of shares of Series A Preferred Stock will have the right to receive $25.00 per share of Series A Preferred Stock, plus accrued and unpaid dividends (whether or not authorized or declared) up to but not including the date of payment, before any payment is made to holders of Common Stock and any other class or series of capital stock ranking junior to Series A Preferred Stock as to liquidation rights. The rights of holders of shares of the Series A Preferred Stock to receive their liquidation preference will be subject to the proportionate rights of any other class or series of our capital stock ranking on parity with the Series A Preferred Stock as to liquidation and junior to the rights of any class or series of our capital stock expressly designated as ranking senior to the Series A Preferred Stock.

We may not redeem the Series A Preferred Stock prior to December 12, 2017, except in limited circumstances to preserve our status as a REIT, and pursuant to the special optional redemption provision described below. On and after December 12, 2017, the Series A Preferred Stock will be redeemable at our option, upon not fewer than 30 and not more than 60 days’ written notice, in whole or in part, at any time or from time to time, for cash at a redemption price of $25.00 per share, plus accrued and unpaid dividends (whether or not authorized or declared) up to, but not including, the redemption date, without interest. If fewer than all the outstanding shares of the Series A Preferred Stock are to be redeemed, the shares to be redeemed

shall be selected pro rata (as nearly as practicable without creating fractional shares) or by any other equitable method we may choose (including by electing to redeem only those shares of Series A Preferred Stock tendered for conversion pursuant to a Change of Control Conversion Right (as defined below)).

Upon the occurrence of a Change of Control (as defined below), we may, at our option, redeem the Series A Preferred Stock, in whole or in part within 120 days after the first date on which such Change of Control occurred, by paying $25.00 per share, plus any accrued and unpaid dividends to, but not including, the date of redemption. If, prior to the Change of Control Conversion Date (as defined below), we exercise any of our redemption rights relating to the Series A Preferred Stock (whether its optional redemption right or special optional redemption right), the holders of Series A Preferred Stock will not have the conversion right described below with respect to the shares called for redemption.

Upon the occurrence of a Change of Control, each holder of Series A Preferred Stock will have the right (unless, prior to the Change of Control Conversion Date, we have provided or provide notice of our election to redeem the Series A Preferred Stock) to convert some or all of the Series A Preferred Stock held by such holder (the “Change of Control Conversion Right”), on the Change of Control Conversion Date into a number of shares of common stock per share of Series A Preferred Stock to be converted equal to the lesser of:

·                   the quotient obtained by dividing (i) the sum of the $25.00 liquidation preference plus the amount of any accrued and unpaid dividends to, but not including, the Change of Control Conversion Date (unless the Change of Control Conversion Date is after a record date for a Series A Preferred Stock dividend payment and prior to the corresponding Series A Preferred Stock dividend payment date, in which case no additional amount for any accrued and unpaid dividend that is to be paid on such dividend payment date will be included in this sum) by (ii) the Common Stock Price (as defined below); and

·                   1.944 (i.e., the Share Cap), subject to certain adjustments;

subject, in each case, to provisions for the receipt of alternative consideration as described in the articles supplementary creating the Series A Preferred Stock.

Upon such a conversion, the holders will be limited to a maximum number of shares of common stock equal to the Share Cap multiplied by the number of shares of Series A Preferred Stock converted. If the Common Stock Price is less than $12.86 (which is approximately 50% of the per-share closing sale price of common stock reported on the New York Stock Exchange, or the NYSE, on December 4, 2012), subject to adjustment, the holders will receive a maximum of 1.944 shares of common stock per share of Series A Preferred Stock, which may result in a holder receiving a value that is less than the liquidation preference of the Series A Preferred Stock.

Within 15 days following the occurrence of a Change of Control, we will provide to holders of record of Series A Preferred Stock a notice of the occurrence of the Change of Control that describes the resulting Change of Control Conversion Right.

If, prior to the Change of Control Conversion Date, we have provided or provide a redemption notice, whether pursuant to our special optional redemption right in connection with a Change of Control or our optional redemption right, holders of Series A Preferred Stock will

not have any right to convert the shares of Series A Preferred Stock selected for redemption in connection with the Change of Control Conversion Right and any shares of Series A Preferred Stock selected for redemption that have been tendered for conversion will be redeemed on the related date of redemption instead of converted on the Change of Control Conversion Date.

A “Change of Control” is when the following have occurred and are continuing:

·                   any person, including any syndicate or group deemed to be a “person” under Section 13(d)(3) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, holds or acquires beneficial ownership, directly or indirectly, through a purchase, merger or other acquisition transaction or series of purchases, mergers or other acquisition transactions of stock of our company entitling that person to exercise more than 50% of the total voting power of all of our stock entitled to vote generally in the election of our directors (except that such person will be deemed to have beneficial ownership of all securities that such person has the right to acquire, whether such right is currently exercisable or is exercisable only upon the occurrence of a subsequent condition); and

·                   following the closing of any transaction referred to in the bullet point above, neither we nor the acquiring or surviving entity has a class of common securities (or American Depositary Receipts, or ADRs, representing such securities) listed on the NYSE, NYSE Amex Equities, or the NYSE Amex, or the NASDAQ Stock Market, or NASDAQ or listed or quoted on an exchange or quotation system that is a successor to the NYSE, the NYSE Amex or NASDAQ.

The “Change of Control Conversion Date” is the date selected by us on which the Series A Preferred Stock is to be converted, which will be a business day that is no fewer than 25 days nor more than 40 days after the date on which we provide the notice described above to the holders of Series A Preferred Stock.

The “Common Stock Price” will be (i) if the consideration to be received in the Change of Control by holders of common stock is solely cash, the amount of cash consideration per share of Common Stock or (ii) if the consideration to be received in the Change of Control by holders of Common Stock is other than solely cash (x) the average of the closing sale prices per share of Common Stock on the principal U.S. securities exchange on which Common Stock is then traded (or, if no closing sale price is reported, the average of the closing bid and ask prices or, if more than one in either case, the average of the average closing bid prices and the average closing ask prices) for the ten consecutive trading days immediately preceding, but not including, the effective date of the Change of Control as reported on the principal U.S. securities exchange on which Common Stock is then traded, or (y) the average of the last quoted bid prices for Common Stock in the over-the-counter market as reported by Pink Sheets LLC or similar organization for the ten consecutive trading days immediately preceding, but not including, the effective date of the Change of Control, if Common Stock is not then listed for trading on a U.S. securities exchange.

The foregoing description of the Articles Supplementary is a summary and, as such, does not purport to be complete and is qualified in its entirety by reference to the full text of the Articles Supplementary, which is attached as Exhibit 3.2 to our Form 8-A filed with the SEC on December 11, 2012, which is incorporated herein by reference.

Exhibit 99.3

SUPPLEMENT TO RESTRICTIONS ON OWNERSHIP AND TRANSFER

This discussion is a supplement to, and is intended to be read together with, the discussion under the heading “Restrictions on Ownership and Transfer” in the Registration Statement on Form S-3 (File No. 333-177052) of CoreSite Realty Corporation (the “Company”) filed with the Securities and Exchange Commission on September 28, 2011 (the “Registration Statement) and in the related prospectus dated October 11, 2011 (the “Base Prospectus”) of the Company. This discussion is not complete and is subject to, and qualified in its entirety by reference to, Maryland law and the Company’s charter and bylaws, which are available as described under “Where You Can Find More Information” in the Base Prospectus.

The following discussion supersedes the fifth paragraph in the discussion under the heading “Restrictions on Ownership and Transfer” in the Base Prospectus.

Our charter contains restrictions on the ownership and transfer of any shares of our common stock, Series A Preferred Stock and capital stock that are intended, among other purposes, to assist us in complying with these requirements and continuing to qualify as a REIT. The relevant sections of our charter and the articles supplementary creating our Series A Preferred Stock provide that, subject to the exceptions described below, no person or entity may actually or beneficially own, or be deemed to own by virtue of the applicable constructive ownership provisions of the Code, more than 9.8% (in value or in number of shares, whichever is more restrictive) of the outstanding shares of our common stock, or the common stock ownership limit, more than 9.8% (in value or in number of shares, whichever is more restrictive) of the outstanding shares of our Series A Preferred Stock, or the preferred stock ownership limit, or 9.8% (in value) of the aggregate of the outstanding shares of our capital stock, or the aggregate stock ownership limit. For purposes of determining the percentage ownership of our capital stock by any person, warrants and rights to acquire capital stock that are treated as owned by that person are deemed outstanding. The value and number of the outstanding shares of our common stock and Series A Preferred Stock and the value of the outstanding shares of capital stock will be determined by the board of directors in good faith, which will be conclusive for all purposes. We refer to these restrictions as the “ownership limits.” In addition, except as a person may be exempted by our board of directors, no person may own capital stock either actually or constructively to the extent that such ownership would cause us to actually or constructively own 10% or more of the ownership interests of any of our tenants or customers. We refer to this as the “tenant limitation.”

The following discussion supersedes the ninth paragraph in the discussion under the heading “Restrictions on Ownership and Transfer” in the Base Prospectus.

Our board of directors may, in its sole discretion, prospectively or retroactively, exempt a person from one or any of the ownership limits and/or tenant limitation. However, our board of directors may not exempt any person whose actual, beneficial or constructive ownership of our outstanding stock would result in our failing to qualify as a REIT. Prior to granting an exemption our board of directors may require the person seeking an exemption to make certain representations and undertakings or to agree that any violation or attempted violation of these restrictions will result in the automatic transfer of the shares of stock causing the violation to the trust described below. Our board of directors may also require a ruling from the Internal Revenue

Service, or the IRS, or an opinion of counsel in order to determine or ensure our status as a REIT and may impose any conditions or restrictions on an exemption as it deems appropriate.

The following discussion supersedes the tenth paragraph in the discussion under the heading “Restrictions on Ownership and Transfer” in the Base Prospectus.

Any attempted transfer of our stock that, if effective, would result in our stock being owned by fewer than 100 persons will be null and void and the intended transferee shall acquire no rights in such shares. Any attempted transfer of our stock which, if effective, would result in a violation of any of the ownership limits or tenant limitation, our being “closely held” under Section 856(h) of the Code (without regard to whether the interest is held during the last half of a taxable year) or our otherwise failing to qualify as a REIT will cause the number of shares of stock causing the violation (rounded up to the nearest whole share) to be automatically transferred to a trustee of a trust for the exclusive benefit of one or more charitable beneficiaries, and the proposed transferee will not acquire any rights in the shares of stock. The automatic transfer will be effective as of the close of business on the business day prior to the date of the attempted transfer or other event that resulted in the transfer to the trust. If a transfer to the trust does not occur or is not automatically effective, for any reason, to prevent a violation of the applicable restrictions on ownership and transfer of our stock, then the attempted transfer that, if effective, would have resulted in a violation of the restrictions on ownership and transfer of our stock will be null and void and the intended transferee shall acquire no rights in such shares.

Exhibit 99.4

SUPPLEMENT TO CERTAIN PROVISIONS OF MARYLAND LAW AND OF OUR CHARTER AND BYLAWS

This discussion is a supplement to, and is intended to be read together with, the discussion under the heading “Certain Provisions of Maryland Law and of our Charter and Bylaws” in the Registration Statement on Form S-3 (File No. 333-177052) of CoreSite Realty Corporation (the “Company”) filed with the Securities and Exchange Commission on September 28, 2011 (the “Registration Statement) and in the related prospectus dated October 11, 2011 (the “Base Prospectus”) of the Company. This discussion is not complete and is subject to, and qualified in its entirety by reference to, Maryland law and the Company’s charter and bylaws, which are available as described under “Where You Can Find More Information” in the Base Prospectus.

The following discussion supersedes the discussion under the heading “Certain Provisions of Maryland Law and of our Charter and Bylaws—Board of Directors” in the Base Prospectus.

Our charter provides that the number of directors may be increased or decreased by a majority vote of our entire board of directors pursuant to our bylaws, but shall never be less than the minimum number required by the MGCL. Our bylaws provide a majority of our entire board may increase or decrease the number of directors, provided that the number of directors may not be decreased to fewer than the minimum number required under the MGCL, which is one, nor increased to more than 15. Any and all vacancies on our board of directors may be filled by the affirmative vote of a majority of the remaining directors, even if less than a quorum, except that a vacancy resulting from an increase in the size of the board of directors must be filled by a majority vote of the entire board of directors, and any individual elected to fill such vacancy will serve until the next annual meeting of stockholders and until a successor is duly elected and qualifies.

Our bylaws require that nominees for director, whether for election by the stockholders or by the board of directors, shall include such number of individuals as are entitled to be nominated pursuant to the partnership agreement. See “Description of Partnership Agreement of CoreSite, L.P. — Board of Directors.” Each of our directors will be elected by our stockholders to serve until the next annual meeting of stockholders and until his or her successor is duly elected and qualifies. A plurality of all votes cast on the matter at a meeting of stockholders at which a quorum is present is sufficient to elect a director. The presence in person or by proxy of stockholders entitled to cast a majority of all the votes entitled to be cast at a meeting constitutes a quorum.

The following discussion supersedes the second paragraph in the discussion under the heading “Certain Provisions of Maryland Law and of our Charter and Bylaws—Advance Notice of Director Nominations and New Business” in the Base Prospectus.

Only the business specified in our notice of the meeting may be brought before a special meeting of our stockholders. Nominations of individuals for election as directors at a special meeting of stockholders must be made (i) by or at the direction of our board of directors, (ii) by a stockholder that has requested a special meeting be called for the purpose of electing directors in

accordance with our bylaws and that has supplied the information required by our bylaws or (iii) if the special meeting has been called in accordance with our bylaws for the purpose of electing directors, by any stockholder who is a stockholder of record both at the time of notice required by our bylaws and the time of the special meeting, is entitled to vote at the meeting in the election of each individual so nominated and has complied with the advance notice requirements of, and provided the information and certifications required by, our bylaws.

The following discussion supersedes the discussion under the heading “Certain Provisions of Maryland Law and of our Charter and Bylaws—Special Meetings of Stockholders” in the Base Prospectus.

Our Chairman, Chief Executive Officer, President, board of directors or any three members of the board of directors may call special meetings of our stockholders. Additionally, our bylaws provide that, subject to the satisfaction of certain procedural and informational requirements by the stockholders requesting the meeting, a special meeting of our stockholders to act on any matter that may properly be considered at a meeting of our stockholders must also be called by our Secretary upon the written request of the stockholders entitled to cast not less than a majority of all the votes entitled to be cast on such matter at the meeting and containing the information and certifications required by our bylaws. Our Secretary will inform the requesting stockholders of the reasonably estimated cost of preparing and mailing the notice of meeting (including our proxy materials), and the requesting stockholder must pay such estimated cost before our Secretary is required to prepare and mail the notice of the special meeting.

The following discussion supersedes the second paragraph in the discussion under the heading “Certain Provisions of Maryland Law and of our Charter and Bylaws—Subtitle 8” in the Base Prospectus.

Through provisions in our charter and bylaws unrelated to Subtitle 8, we already (1) vest in our board of directors the exclusive power, subject to the limitations described above, to fix the number of directors, by vote of a majority of the entire board of directors, and (2) require, unless called by our Chairman of our board of directors, our Chief Executive Officer, our President, our board of directors or any three members of our board of directors, the request of stockholders entitled to cast a majority of votes entitled to be cast on a matter at the meeting to call a special meeting to act on the matter. We have not elected to create a classified board. In the future, our board of directors may elect, without stockholder approval, to create a classified board or elect to be subject to any of the other provisions of Subtitle 8.