What is now Eatontown was originally incorporated as Eatontown Township by an Act of the New Jersey Legislature on April 4, 1873, from portions of Ocean Township and Shrewsbury Township. Portions of the township were taken to form West Long Branch (April 7, 1908) and Oceanport (April 6, 1920). Eatontown was reincorporated as a borough on March 8, 1926, replacing Eatontown Township, based on the results of a referendum held on April 13, 1926.
The United States Army's Fort Monmouth has been in Eatontown since 1917, and is home to the U.S. Army Materiel Command's (AMC) Communication and Electronics Command (CECOM). Fort Monmouth is also home to the United States Military Academy Preparatory School (or USMAPS), which trains approximately 250 students per year to enter as freshmen (plebes) at the United States Military Academy at West Point.