Long Valley is an unincorporated community and census-designated place (CDP) located within Washington Township, in Morris County, New Jersey, United States. Once known as German Valley from its foundation during the colonial era, the community was renamed in response to anti-German sentiment during World War I. As of the 2010 United States Census, the CDP's population was 1,879.
According to the United States Census Bureau, the CDP had a total area of 4.623 square miles (11.974 km2), including 4.566 square miles (11.825 km2) of land and 0.057 square miles (0.148 km2) of water (1.24%).
There are several bodies of water, including several man-made lakes used for agriculture and a portion of the Raritan River that are not reflected in the calculation of water area.
The climate in this area is characterized by hot, humid summers and generally mild to cool winters. According to the Köppen Climate Classification system, Long Valley has a humid subtropical climate, abbreviated "Cfa" on climate maps.
The 2010 United States Census counted 1,879 people, 675 households, and 534 families in the CDP. The population density was 411.5 inhabitants per square mile (158.9/km2). There were 709 housing units at an average density of 155.3 per square mile (60.0/km2). The racial makeup was 94.73% (1,780) White, 0.53% (10) Black or African American, 0.00% (0) Native American, 1.81% (34) Asian, 0.00% (0) Pacific Islander, 1.33% (25) from other races, and 1.60% (30) from two or more races. Hispanic or Latino of any race were 5.32% (100) of the population.
Of the 675 households, 37.0% had children under the age of 18; 65.8% were married couples living together; 9.5% had a female householder with no husband present and 20.9% were non-families. Of all households, 15.6% were made up of individuals and 6.1% had someone living alone who was 65 years of age or older. The average household size was 2.77 and the average family size was 3.10.
25.8% of the population were under the age of 18, 5.9% from 18 to 24, 21.0% from 25 to 44, 34.0% from 45 to 64, and 13.4% who were 65 years of age or older. The median age was 43.8 years.