Washington was incorporated as a township by an Act of the New Jersey Legislature on November 19, 1802, from portions of Evesham Township, Little Egg Harbor Township and Northampton Township (now known as Mount Holly Township, New Jersey). Portions of the township were taken to form Shamong Township (February 19, 1852), Bass River Township (March 30, 1864), Woodland Township (March 7, 1866) and Randolph Township (March 17, 1870, reannexed to Washington Township on March 28, 1893).
There were 160 households out of which 35.6% had children under the age of 18 living with them, 61.3% were married couples living together, 6.3% had a female householder with no husband present, and 29.4% were non-families. 24.4% of all households were made up of individuals and 12.5% had someone living alone who was 65 years of age or older. The average household size was 2.76 and the average family size was 3.27.
In the township the population was spread out with 29.3% under the age of 18, 3.5% from 18 to 24, 23.8% from 25 to 44, 19.0% from 45 to 64, and 24.3% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 92.3 males. For every 100 females age 18 and over, there were 86.8 males.
The median income for a household in the township was $41,250, and the median income for a family was $42,188. Males had a median income of $32,000 versus $31,719 for females. The per capita income for the township was $13,977. About 8.0% of families and 16.0% of the population were below the poverty line, including 22.4% of those under age 18 and 13.9% of those age 65 or over.
Public school students in grades 9 - 12 attend Oakcrest High School, located in Hamilton Township, which serves students from Hamilton Township, Mullica Township, the City of Port Republic and Washington Township. 2,108 students attend the school. The High School is part of the Greater Egg Harbor Regional High School District, a regional high school district serving approximately 3,700 in the Atlantic County districts of Egg Harbor City, Galloway Township, Hamilton Township and Mullica Township, together with students from the City of Port Republic and Washington Township who attend as part of sending/receiving relationships.