Brookside (once called Waterstreet) is a historic unincorporated community and census-designated place (CDP)[9] located within Mendham Township in Morris County, in the U.S. state of New Jersey.

[2] A portion of the Patriots' Path, the trail George Washington and his troops marched on, runs through Brookside's woods along the Whippany River.

[15] The Brookside Post Office, which at one time was also a general store and gas station, is still the social hub of the village.

The district was added to the National Register of Historic Places on February 16, 1996, for its significance in architecture, industry, and community development from 1780 to 1942.

It includes floats made by community groups and families, a lawnmower brigade, fire departments and ambulance squads from all over the region, farm animals, a pooch parade, and both rock and marching bands.

It starts at 9 am from the intersection of Dogwood Drive and Tingley Road, then down East Main Street to the Community Club Field where food, games, and activities for people of all ages await.

The Annual Clam Bake, sponsored by the Brookside Engine Company #1, is also held at the Community Club Field on the second Saturday in September.

Other events and programs are often offered by the Mendham Township Library, located on the 1st floor of the municipal building on West Main Street in Brookside.