Colonia is an unincorporated community and census-designated place (CDP) located within Woodbridge Township, in Middlesex County, New Jersey, United States. As of the 2010 United States Census, the CDP's population was 17,795.
In 1919, the New Jersey State Highway Commission built a new road that became part of the Lincoln Highway, an early plan to create a transcontinental highway. The stretch was constructed on the west side of the Pennsylvania Railroad (now the Northeast Corridor) from near the northeast of Dow Avenue between Colonia and Iselin to Cedar Street in Menlo Park, to avoid two railroad crossings. The old road is now Middlesex-Essex Turnpike and Thornall Street, on the east side of the tracks.
According to the United States Census Bureau, the CDP had a total area of 3.914 square miles (10.137 km2), including 3.910 square miles (10.126 km2) of land and 0.004 square miles (0.011 km2) of water (0.11%).
The 2010 United States Census counted 17,795 people, 6,160 households, and 4,977 families in the CDP. The population density was 4,551.4 inhabitants per square mile (1,757.3/km2). There were 6,321 housing units at an average density of 1,616.7 per square mile (624.2/km2). The racial makeup was 80.37% (14,302) White, 5.26% (936) Black or African American, 0.12% (21) Native American, 10.70% (1,904) Asian, 0.04% (8) Pacific Islander, 1.54% (274) from other races, and 1.97% (350) from two or more races. Hispanic or Latino of any race were 9.27% (1,649) of the population.
Of the 6,160 households, 34.8% had children under the age of 18; 65.6% were married couples living together; 11.3% had a female householder with no husband present and 19.2% were non-families. Of all households, 16.4% were made up of individuals and 8.9% had someone living alone who was 65 years of age or older. The average household size was 2.89 and the average family size was 3.25.
22.8% of the population were under the age of 18, 7.5% from 18 to 24, 24.4% from 25 to 44, 30.0% from 45 to 64, and 15.3% who were 65 years of age or older.