Green Brook Park is a 100-acre (40 ha) county park along the Green Brook, a tributary of the Raritan River, in the city of Plainfield in Union County, New Jersey.

Designed by the Olmsted Brothers, it was added to the National Register of Historic Places on May 14, 2004, for its significance in landscape architecture.

It extends into the borough of North Plainfield in Somerset County.

[3] The Union County Park Commission was established in 1921 and hired the Olmsted Brothers, formed by the sons of landscape architect Frederick Law Olmsted, to design a county park system, including this one along the Green Brook.

The park was expanded east of West End Avenue during the 1930s.