What is now Clayton was originally formed as Clayton Township, which was created on February 5, 1858, from portions of Franklin Township. Portions of the township were taken to form Glassboro Township on March 11, 1878. Clayton was formed as a borough by an Act of the New Jersey Legislature on May 9, 1887, from portions of Clayton Township. The remainder of Clayton Township was absorbed by the Borough of Clayton on April 14, 1908, and the township was dissolved.
According to the United States Census Bureau, the borough has a total area of 7.3 square miles (19.0 km²), of which, 7.2 square miles (18.6 km²) of it is land and 0.2 square miles (0.4 km²) of it (2.31%) is water.
There were 2,464 households out of which 39.4% had children under the age of 18 living with them, 57.5% were married couples living together, 13.9% had a female householder with no husband present, and 23.5% were non-families. 19.7% of all households were made up of individuals and 7.5% 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 3.31.
In the borough the population was spread out with 29.1% under the age of 18, 8.7% from 18 to 24, 31.6% from 25 to 44, 21.0% from 45 to 64, and 9.6% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 91.7 males. For every 100 females age 18 and over, there were 89.8 males.
The median income for a household in the borough was $53,219, and the median income for a family was $63,097. Males had a median income of $37,231 versus $29,063 for females. The per capita income for the borough was $20,006. About 3.1% of families and 2.9% of the population were below the poverty line, including 4.0% of those under age 18 and 1.7% of those age 65 or over.
The Mayor of the Borough of Clayton is Melissa Hoffman (2011). Members of the Borough Council are Tom Bianco (2010), Steven Carr (2009), Craig Conti (2008), Kim Robinson (2009), Tony Saban (2010) and Leslie Wise (2008).