Sayreville was originally incorporated as a township on April 6, 1876, from portions of South Amboy Township. On April 2, 1919, the borough was reincorporated as the Borough of Sayreville, based on the results of a referendum held on April 29, 1919. In 2007, Sayreville ranked 47 among the top 100 places to live in the United States by Money Magazine.
As of the census of 2000, there were 40,377 people, 14,955 households, and 10,917 families residing in the borough. The population density was 2,539.4 people per square mile (980.5/km²). There were 15,235 housing units at an average density of 958.1/sq mi (370.0/km²). The racial makeup of the borough was 76.47% White, 8.62% African American, 0.13% Native American, 10.56% Asian, 0.02% Pacific Islander, 2.12% from other races, and 2.08% from two or more races. Hispanic or Latino of any race were 7.29% of the population.
There were 14,955 households out of which 34.3% had children under the age of 18 living with them, 57.5% were married couples living together, 11.1% had a female householder with no husband present, and 27.0% were non-families. 22.3% of all households were made up of individuals and 8.7% had someone living alone who was 65 years of age or older. The average household size was 2.68 and the average family size was 3.17.
In the borough the population was spread out with 23.6% under the age of 18, 7.3% from 18 to 24, 34.2% from 25 to 44, 22.5% from 45 to 64, and 12.4% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 96.3 males. For every 100 females age 18 and over, there were 92.0 males.
The median income for a household in the borough was $58,919, and the median income for a family was $66,266 (these figures had risen to $68,762 and $81,778 respectively as of a 2007 estimate). Males had a median income of $47,427 versus $35,151 for females. The per capita income for the borough was $24,736. About 3.4% of families and 4.7% of the population were below the poverty line, including 6.1% of those under age 18 and 5.3% of those age 65 or over.
Sayreville enjoys proximity to several major roadways - the Garden State Parkway, New Jersey Turnpike (Interstate 95), Interstate 287 which becomes Route 440 — providing access to Staten Island and Long Island, New York points — U.S. 1, U.S. 9, Route 18, Route 34, Route 35 and Route 36.
Three highway bridges span the Raritan River from the Sayreville side. The Edison Bridge on U.S. 9 and the Driscoll Bridge on the Garden State Parkway connect Woodbridge on the north with Sayreville on the south. The Victory Bridge carries Route 35, connecting Sayreville with Perth Amboy.
New Jersey Transit offers service to the Port Authority Bus Terminal in Midtown Manhattan via the 131 and 139. Service within New Jersey is offered to Newark on the 67, to Jersey City on the 64, and to other local destinations on the 815 and 817 routes.