CoreSite Realty Corporation (NYSE: COR), an owner, developer and operator of strategically located data centers in some of the leading communications hubs in North America, today announced the closing of an underwritten public offering of 4,600,000 shares of 7.25% Series A Cumulative Redeemable Preferred Stock (the “Series A Preferred Stock”) at a price of $25.00 per share for net proceeds of approximately $111 million, after deducting underwriting discounts and commissions and expenses. The 4,600,000 shares of the Company’s Series A Preferred Stock includes the underwriters’ exercise of their over-allotment option on December 7, 2012 to purchase an additional 600,000 shares of the Company’s Series A Preferred Stock. The Series A Preferred Stock is expected to be admitted for trading on the New York Stock Exchange under the symbol “CORprA” within 30 days of the date of closing.

The Company intends to contribute the net proceeds from this offering to its operating partnership, CoreSite, L.P., which will subsequently use the net proceeds received from the Company to temporarily repay borrowings under its revolving credit facility, to repay the full amount of the mortgage loan payable on its 12100 Sunrise Valley property and for general corporate purposes, which could include the acquisition of additional properties or to fund development and redevelopment opportunities. The offering is being made pursuant to an effective shelf registration statement, prospectus and related prospectus supplement filed by the Company with the Securities and Exchange Commission.

Citigroup Global Markets Inc., Merrill Lynch, Pierce, Fenner & Smith Incorporated and RBC Capital Markets, LLC are the joint book-running managers for the offering. Credit Suisse Securities (USA) LLC and KeyBanc Capital Markets Inc. are the co- managers for the offering.

A copy of the prospectus supplement and the accompanying prospectus relating to these securities may be obtained, when available, by contacting Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717 (tel: 800-831-9146) or email: batprospectusdept@citi.com; Merrill Lynch, Pierce, Fenner & Smith Incorporated, 222 Broadway, 7th Floor, New York, NY 10038, attention: Prospectus Department, or e-mail dg.prospectus_requests@baml.com. Phone: 1-800-294-1322; RBC Capital Markets, LLC, Attention: Prospectus Department, Three World Financial Center, 200 Vesey Street, 8th floor, New York, New York 10281-8098, (866) 375-6829, rbcnyfixedincomeprospectus@rbccm.com; Credit Suisse Securities (USA) LLC, One Madison Avenue, New York, NY 10010, Attn: Prospectus Department. Phone: 1-800-221-1037; KeyBanc Capital Markets Inc., Phone: (866) 227-6479.

This press release is for informational purposes only and is not an offer to sell or the solicitation of an offer to buy with respect to any securities in any jurisdiction in which such offer, solicitation or sale would be unlawful. The offering is not being made in any jurisdiction in which the making or acceptance thereof would not be in compliance with the securities, blue sky or other laws of such jurisdiction.

About CoreSite

CoreSite Realty Corporation (NYSE: COR) is an owner, developer and operator of strategically located data centers in some of the leading communications hubs in North America. These locations are among the largest and fastest growing data center markets in the United States, including Los Angeles, the San Francisco Bay and Northern Virginia areas, Chicago, Boston, New York City, Miami, Denver, and Washington, DC. CoreSite works with a broad and growing customer base of over 750 customers, including network and mobility services providers, cloud service providers, digital content organizations, systems integrators, managed service providers and enterprise customers of all sizes with a variety of space, power and interconnection needs. As of September 30, 2012, CoreSite’s property portfolio included 14 operating data center facilities and one development site, which collectively comprise over 2.1 million net rentable square feet, or NRSF, of which approximately 1.2 million NRSF represented existing data center space.

Forward Looking Statements

This press release contains forward-looking statements which are based on current expectations, forecasts and assumptions that involve risks and uncertainties that could cause actual outcomes and results to differ materially. Such forward-looking statements include statements related to the completion and timing of the offering, the intended use of proceeds from the offering and the intended listing of the shares on the New York Stock Exchange. These risks and uncertainties include, among others, the following: the geographic concentration of CoreSite’s data centers in certain markets and any adverse developments in local economic conditions or the demand for data center space in these markets; fluctuations in interest rates and increased operating costs; difficulties in identifying properties to acquire and completing acquisitions; significant industry competition; CoreSite’s failure to obtain necessary outside financing; CoreSite’s failure to qualify or maintain its status as a REIT; financial market fluctuations; changes in real estate and zoning laws and increases in real property tax rates; and other factors affecting the real estate industry generally. For a further list and description of such risks and uncertainties, see the reports and other filings by the Company with the U.S. Securities and Exchange Commission, including the Company’s Annual Report on Form 10-K for the year ended December 31, 2011. The Company disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.