UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-Q

For the quarterly period ended September 30, 2012

or

For transition period from                to

Commission File Number 333-181995

NORTHFIELD BANCORP, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (732) 499-7200

Not Applicable

(Former name, former address, and former fiscal year, if changed since last report)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.     (1) Yes  þ    No  ¨.     (2) Yes  ¨    No  þ.

Indicate by check mark whether the registrant has submitted electronically and posted on it corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for shorter period that the registrant was required and post such files).     Yes  ¨    No  ¨.

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definitions of “large accelerated filer,” “accelerated filer,” and “smaller reporting company” in Rule 12b-2 of the Exchange Act (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).     Yes  ¨    No  þ.

Indicate the number of shares outstanding of each of the issuer’s classes of common stock as of the latest practicable date. As of December 21, 2012, zero shares of Common Stock, par value $0.01 per share.

EXPLANATORY NOTE

Northfield Bancorp, Inc., a Delaware corporation (the “Company”), was formed to serve as the stock holding company for Northfield Bank as part of the mutual-to-stock conversion of Northfield Bancorp, MHC. The Company is offering shares of common stock for sale in connection with the conversion of Northfield Bancorp, MHC from the mutual holding company to the stock holding company form of organization. The shares we are offering represent the ownership interest in Northfield Bancorp, Inc., a federal corporation, currently owned by Northfield Bancorp, MHC. As of September 30, 2012, the conversion had not been completed, and, as of that date, the Company had no assets or liabilities, and had not conducted any business other than that of an organizational nature. For informational purposes, please see the Quarterly Report for the quarter ended September 30, 2012 of Northfield Bancorp, Inc., a federal corporation and the current stock holding company for the Bank, which has previously been filed with the U.S. Securities and Exchange Commission.

PART I – FINANCIAL INFORMATION

Please see the Explanatory Note.

Please see the Explanatory Note.

Please see the Explanatory Note.

Under the supervision and with the participation of our management, including our Chief Executive Officer and Chief Financial Officer, we evaluated the effectiveness of the design and operation of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934) as of the end of the period covered by this report. Based upon that evaluation, the Chief Executive Officer and Chief Financial Officer concluded that, as of the end of the period covered by this report, our disclosure controls and procedures were effective.

During the quarter ended September 30, 2012, there were no changes in the Company’s internal control over financial reporting that have materially affected, or are reasonably likely to materially affect, the Company’s internal control over financial reporting.

Please see the Explanatory Note.

PART II – OTHER INFORMATION

Please see the Explanatory Note.

There have been no material changes in the “Risk Factors” disclosed in the Company’s Registration Statement on Form S-1 (Commission File No. 333-181995).

Please see the Explanatory Note.

Please see the Explanatory Note.

Not applicable.

None

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 thereunto duly authorized.