UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) the

Securities Exchange Act of 1934

Date of report (Date of earliest event reported): October 16, 2017

CoreSite Realty Corporation

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code:  (866) 777-2673

N/A

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

o                 Written communication pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o                 Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o                 Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o                 Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 or Rule 12b-2 of the Securities Exchange Act of 1934.

Emerging growth company o

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Item 8.01                                           Other Events.

On October 16, 2017, CoreSite Realty Corporation, a Maryland corporation, announced that it will redeem all 4,600,000 shares of its 7.25% Series A Cumulative Redeemable Preferred Stock, $0.01 par value per share (the “Series A Preferred Stock”) (NYSE: COR.PRA — CUSIP No. 21870Q 204), on December 12, 2017. The Series A Preferred Stock will be redeemed at the redemption price of $25.00 per share, plus $0.292014 in accrued and unpaid dividends on each share.

A copy of the press release announcing the redemption of the Series A Preferred Stock is hereby incorporated by reference and attached hereto as Exhibit 99.1.

Item 9.01                                           Financial Statements and Exhibits.

(d)                                 Exhibits

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EXHIBIT INDEX

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Dated:           October 16, 2017

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