Harmony is an unincorporated community and census-designated place (CDP) located within Harmony Township in Warren County, in the U.S. state of New Jersey, that was defined as part of the 2010 United States census. As of the 2010 Census, the CDP's population was 441.
According to the United States Census Bureau, the CDP had a total area of 1.240 square miles (3.210 km<sup>2</sup>), all of which was land.
Harmony first appeared as a census designated place in the 2010 U.S. census.
The 2010 United States census counted 441 people, 166 households, and 126 families in the CDP. The population density was . There were 180 housing units at an average density of . The racial makeup was 98.19% (433) White, 0.68% (3) Black or African American, 0.00% (0) Native American, 0.00% (0) Asian, 0.00% (0) Pacific Islander, 0.23% (1) from other races, and 0.91% (4) from two or more races. Hispanic or Latino of any race were 0.68% (3) of the population.
Of the 166 households, 28.9% had children under the age of 18; 65.7% were married couples living together; 7.2% had a female householder with no husband present and 24.1% were non-families. Of all households, 21.7% were made up of individuals and 11.4% had someone living alone who was 65 years of age or older. The average household size was 2.66 and the average family size was 3.10.
21.5% of the population were under the age of 18, 7.3% from 18 to 24, 18.4% from 25 to 44, 39.0% from 45 to 64, and 13.8% who were 65 years of age or older. The median age was 46.2 years. For every 100 females, the population had 93.4 males. For every 100 females ages 18 and older there were 97.7 males.