Monroe Township was founded in 1838 and named in honor of the President of the United States
James Monroe. For many decades, it was largely a farming community; when parts of the township blossomed into the more densely-packed neighborhoods of Helmetta, Jamesburg, and Spotswood in the late 19th century, they seceded. Railroads came into Monroe from just about the very beginning, starting with the Camden and Amboy Rail Road in the 1830s and 1840s.

The 2010 United States Census reported that there were 39,132 people, 16,497 households and 10,877 families residing in the township. The racial makeup of Monroe Township was 81.6% (31,913) White, 3.9% (1,533) African American, 0.1% (33) Native American, 12.6% (4,930) Asian, 0.0% (4) Pacific Islander, 0.6% (244) from other races, and 1.2% (475) from two or more races. Hispanic or Latino of any race were 4.3% (1,673). The population estimate December 2012 - 40,795.

Monroe Township is governed by the Mayor-Council system of New Jersey municipal government under the Faulkner Act.

As of 2017, the Mayor of Monroe Township is Gerald Tamburro (D). Members of the Borough Council are Council President Stephen Dalina (D) (at-large) Elizabeth Schneider (D)(Ward 1), Blaise Dipierro (D)(Ward 2), Michael Leibowitz(D)(Ward 3) and Miriam Cohen(D) (at-large).

Monroe Township is in the 12th Congressional district. New Jersey's Twelfth Congressional District is represented by Bonnie Watson-Coleman (D), New Jersey is represented in the United States Senate by Cory Booker (D),  and Bob Menendez (D).

Monroe Township is in the The 14th district of the New Jersey Legislature is represented in the State Senate by Linda R. Greenstein (D), Plainsboro Township and in the General Assembly by Daniel R. Benson (D), Hamilton Township, Mercer County and Wayne DeAngelo (D), Hamilton Township, Mercer County.

Middlesex County is governed by a Board of Chosen Freeholders, whose seven members are elected at-large to serve three-year terms of office on a staggered basis, with two or three seats.