Washington is a borough in Warren County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 6,461, reflecting a decline of 251 (-3.7%) from the 6,712 counted in the 2000 Census, which had in turn increased by 238 (+3.7%) from the 6,474 counted in the 1990 Census. The borough is located in the easternmost region of the Lehigh Valley.
Washington was incorporated as a borough by an act of the New Jersey Legislature on February 20, 1868, from portions of Washington Township. The borough was named for George Washington, one of more than ten communities statewide named for the first president. The Borough of Washington is surrounded by Washington Township, which is one of five municipalities in the state of New Jersey with the name "Washington Township".
Washington Borough separated from Washington Township as of February 20, 1868. The community grew during the 19th century as a result of the transportation routes that ran through or near the borough. The Morris Canal ran along the north end of town and two rail lines of the Delaware, Lackawanna and Western Railroad crossed within the borough. Intersecting in the center of the borough are two major roadways, which today are Route 31 and Route 57. The borough was ultimately named for the "Washington House", a tavern built by Revolutionary War Col.