According to the United States Census Bureau, the township had a total area of 42.19 square miles (109.26 km²), including 41.94 square miles (108.63 km²) of land and 0.24 square miles (0.63 km²) of water (0.58%).
It is the largest municipality in Middlesex County in terms of total area.

Clearbrook Park (with a 2010 population of 2,667), Concordia (3,092 in 2010), Rossmoor (2,666 as of 2010), and Whittingham (2,476 in 2010) are unincorporated communities and census-designated places (CDPs) located within Monroe Township.

Monroe completely surrounds Jamesburg, making it part of 21 pairs of "doughnut towns" in the state, where one municipality entirely surrounds another.
The township borders Cranbury Township, East Brunswick Township, Helmetta, Old Bridge Township, South Brunswick Township, and Spotswood in Middlesex County; East Windsor Township in Mercer County; and Manalapan Township and Millstone Township in Monmouth County.
According to the United States Census Bureau, the township had a total area of 42.19 square miles (109.26 km²), including 41.94 square miles (108.63 km²) of land and 0.24 square miles (0.63 km²) of water (0.58%). It is the largest municipality in Middlesex County in terms of total area.
Clearbrook Park (with a 2010 population of 2,667), Concordia (3,092 in 2010), Rossmoor (2,666 as of 2010), and Whittingham (2,476 in 2010) are unincorporated communities and census-designated places (CDPs) located within Monroe Township.
Monroe completely surrounds Jamesburg, making it part of 21 pairs of "doughnut towns" in the state, where one municipality entirely surrounds another. The township borders Cranbury Township, East Brunswick Township, Helmetta, Old Bridge Township, South Brunswick Township, and Spotswood in Middlesex County; East Windsor Township in Mercer County; and Manalapan Township and Millstone Township in Monmouth County.
Monroe Township, Middlesex County, New Jersey