UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) December 19, 2013

Rockville Financial, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (860) 291-3600

Not Applicable

(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:

On December 19, 2013, Rockville Financial, Inc. (“Rockville”) and United Financial Bancorp, Inc. (“United”) issued a joint press release announcing the proposed consolidation of four branches in connection with the pending merger of Rockville and United.

The press release announcing branch consolidations is included as Exhibit 99.1 to this report and incorporated herein by reference.

Cautionary Statements Regarding Forward-Looking Information

This Current Report on Form 8-K contains forward looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 giving Rockville’s or United’s expectations or predictions of future financial or business performance or conditions. Forward-looking statements are typically identified by words such as “believe,” “expect,” “anticipate,” “intend,” “target,” “estimate,” “continue,” “positions,” “prospects” or “potential,” by future conditional verbs such as “will,” “would,” “should,” “could” or “may”, or by variations of such words or by similar expressions. Such forward-looking statements include, but are not limited to, statements about the benefits of the business combination transaction involving United and Rockville, including future financial and operating results, the combined company’s plans, objectives, expectations and intentions and other statements that are not historical facts. These forward-looking statements are subject to numerous assumptions, risks and uncertainties which change over time. Forward-looking statements speak only as of the date they are made and neither Rockville nor United assumes any duty to update forward-looking statements. In addition to factors previously disclosed in Rockville’s and United’s reports filed with the Securities and Exchange Commission, the following factors, among others, could cause actual results to differ materially from forward-looking statements: ability to obtain regulatory approvals and meet other closing conditions to the merger, including approval by Rockville and United shareholders, on the expected terms and schedule; delay in closing the merger; difficulties and delays in integrating the Rockville and United businesses or fully realizing cost savings and other benefits; business disruption following the proposed transaction; changes in asset quality and credit risk; the inability to sustain revenue and earnings growth; changes in interest rates and capital markets; inflation; customer borrowing, repayment, investment and deposit practices; customer disintermediation; the introduction, withdrawal, success and timing of business initiatives; competitive conditions; the inability to realize cost savings or revenues or to implement integration plans and other consequences associated with mergers, acquisitions and divestitures; economic conditions; changes in Rockville’s stock price before closing, including as a result of the financial performance of United prior to closing; the reaction to the transaction of the companies’ customers, employees and counterparties; and the impact, extent and timing of technological changes, capital management activities, and other actions of the Federal Reserve Board and legislative and regulatory actions and reforms.

Annualized, pro forma, projected and estimated numbers are used for illustrative purpose only, are not forecasts and may not reflect actual results.

Additional Information for Stockholders

In connection with the proposed merger, Rockville has filed with the Securities and Exchange Commission (“SEC”) a Registration Statement on Form S-4 that includes a preliminary joint proxy statement of Rockville and United and a preliminary prospectus of Rockville, as well as other relevant documents concerning the proposed transaction. Rockville and United will mail the definitive joint proxy statement/prospectus to their stockholders. SHAREHOLDERS OF ROCKVILLE AND UNITED ARE URGED TO READ THE REGISTRATION STATEMENT AND JOINT PROXY STATEMENT/PROSPECTUS REGARDING THE PROPOSED MERGER WHEN IT BECOMES AVAILABLE AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THOSE DOCUMENTS, BECAUSE THEY CONTAIN IMPORTANT INFORMATION. Investors and security holders may obtain a free copy of the proxy statement/prospectus (when available) and other filings containing information about Rockville and United at the SEC’s website at www.sec.gov. The joint proxy statement/prospectus (when available) and the other filings may also be obtained free of charge at Rockville’s website at www.rockvillefinancialinc.com under the section “SEC Filings” or at United’s website at www.bankatunited.com under the tab “About Us” and then “Investor Relations,” and then under the heading “SEC Filings.”

Rockville, United and certain of their respective directors and executive officers, under the SEC’s rules, may be deemed to be participants in the solicitation of proxies of Rockville’s and United’s shareholders in connection with the proposed merger. Information about the directors and executive officers of Rockville and their ownership of Rockville common stock is set forth in the proxy statement for Rockville’s 2013 Annual Meeting of Shareholders, as filed with the SEC on Schedule 14A on April 4, 2013. Information about the directors and executive officers of United and their ownership of United common stock is set forth in the proxy statement for United’s 2013 Annual Meeting of Shareholders, as filed with the SEC on a Schedule 14A on March 13, 2013. Additional information regarding the interests of those participants and other persons who may be deemed participants in the transaction may be obtained by reading the joint proxy statement/prospectus regarding the proposed merger when it becomes available. Free copies of this document may be obtained as described in the preceding paragraph.

SIGNATURES

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.

Exhibit Index