The banks have inked a definitive agreement to this effect in August last year.
With this acquisition, Northfield expands its footprint into Mercer and Hunterdon counties in New Jersey, bringing the number of its branches to 18.
Hopewell Valley Community Bank will operate as a part of Northfield Bank and it will assume the Northfield Bank name and brand, upon completion of the integration of the data processing systems in April this year.
Northfield and Hopewell Valley will have combined assets of $3.6bn, loans of $2.6bn, and deposits of $2.4bn.
Northfield Bank chairman and CEO John W. Alexander said: "This partnership unites two banks that are known for their superior customer and community service.
"We are excited to expand our New Jersey franchise and welcome the Hopewell Valley customers and employees to the Northfield family."
Under the agreed terms, Hopewell Valley shareholders would receive either 0.9592 shares of Northfield common stock or $14.50 in cash for each share of common stock of Hopewell Valley.
In addition to New Jersey, Northfield operates 12 branch locations in Staten Island, New York and nine branch locations in Brooklyn, New York.
Hopewell Valley president and CEO James Hyman previously said: "Northfield is a bank that shares our dedication to customer service. Additionally, through this partnership, we will be able to bring additional products and services, and lending capacity to our customers."