Martinsville is an unincorporated community and census-designated place (CDP)[11] located within Bridgewater Township, in Somerset County, in the U.S. state of New Jersey.

It is an affluent, predominantly residential area, though it does have its own commercial center along Washington Valley Road, and its own post office.

Its position provided a natural fortress not only protecting the Continental Army, but also overlooking the plains towards New Brunswick where the British forces were stationed in 1777.

By special order of Congress, a Thirteen Star Flag is flown 24 hours a day at the Washington Camp Ground, part of the former Middlebrook encampment, in Bridgewater.

Little Friends of Jesus Nursery School (preschool, non-parochial) operate under the supervision of Roman Catholic Diocese of Metuchen.