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.

The borough was ultimately named for the "Washington House", a tavern built by Revolutionary War Col. William McCullough in 1811 that was later destroyed by fire in 1869.

The advent of the automobile brought Washington closer to both the Lehigh Valley and New York City.

In the years following World War II, the population increased, and there were many new houses and apartment complexes built.

Upper Pohatcong Mountain extends northeast of Washington approximately 6 mi (9.7 km) to the vicinity of Hackettstown.

The 2010 United States census counted 6,461 people, 2,623 households, and 1,668 families in the borough.

[39][40] Notable annual events include Washington Celebrates America, which takes place every July 4;[42] Warren Arts and Craft Beer Festival, held every year in April;[43] and Festival in the Borough, which takes place every September.

[7][46][47] As of 2023[update], the borough's Mayor is Democrat Ethel Conry, who was elected to serve an unexpired term of office ending on December 31, 2024.

[3] Members of the Borough Council are Deputy mayor Louann M. Cox (Republican, 2024), Jerry Brown (R, 2026), Edward France (R, 2026), Cassandra Gorshkov (R, 2026), Christopher Infinito (R, 2024;appointed to an unexpired term) and Sherri Musick (R, 2026).

[48][49][50][51] In January 2022, the borough council appointed Sonia Ron to fill the seat expiring in December 2022 that had been held by Chelsea Duchemin.

[52] Following the resignation of Mayor David Higgins in December 2021, the borough council voted the following month to leave the position vacant until the November 2022 general election, when voters will choose a candidate to serve the balance of the term of office through December 2024.

[50] In January 2017, Paul Jones was selected on an interim basis to fill the seat expiring in December 2018 that became vacant when David Higgins took office as mayor.

[54] Dewayne Keith Norris was elected in November 2017 to fill the vacant seat for the remainder of the term of office.

The council passed a symbolic no confidence vote by a 4-2 margin, though Norris indicated that he was unwilling to resign from office.

[56] Kristine Henry, who had served as Washington's clerk and borough manager, was sentenced in January 2018 to seven years in jail, lost her ability to work in a public job and was required to repay $97,000 she had stolen from the borough after writing a series of checks payable to herself from 2011 to 2016.

Her role was filled by Matthew Hall, who was the borough's manager for several years and helped improve the town's sewers, garbage collection system, and paved the way for new businesses and residences to be built in the area.

[59][60][61] For the 119th United States Congress, New Jersey's 7th congressional district is represented by Thomas Kean Jr. (R, Westfield).

[63] For the 2024-2025 session, the 23rd legislative district of the New Jersey Legislature is represented in the State Senate by Doug Steinhardt (R, Lopatcong Township) and in the General Assembly by John DiMaio (R, Hackettstown) and Erik Peterson (R, Franklin Township).

[68][69] Constitutional officers of Warren County are: Clerk Holly Mackey (R, Alpha; 2027),[70][71] Sheriff James McDonald Sr. (R, Phillipsburg; 2025)[72][73] and Surrogate Michael J. Doherty (R, Washington; 2025).

[77] Among the borough's 2010 Census population, 58.7% (vs. 62.3% in Warren County) were registered to vote, including 77.1% of those ages 18 and over (vs. 81.5% countywide).