Mansfield Township is a rural township in Warren County, New Jersey, occupying roughly 30 square miles of ridges, valleys, and farmland along the Musconetcong River in the state's northwestern corner. Founded in 1754, it is the oldest municipality in Warren County, which was itself carved out of Sussex County in 1824. The township's early history is rooted in agriculture and milling, and its landscape still reflects that heritage through working farms, stone farmhouses, and small crossroads hamlets. The township sits in the Musconetcong River valley, with the river forming part of its boundary. In 2006 the Musconetcong was designated a National Wild and Scenic River, a recognition of its water quality and its role in the region's ecology and recreation. The river remains a focal point for fishing, paddling, and riverside trails, and its banks anchor the Warren Heritage Scenic Byway that winds through the area. Mansfield's population has grown modestly over the decades, reaching about 7,800 residents at the 2020 census, the highest count in its history. The community is largely residential and agricultural, appealing to residents seeking a quieter pace within commuting distance of the larger employment centers of northwestern New Jersey and the Lehigh Valley. Historic Beattystown, one of the township's early settlement nodes, retains examples of its 18th- and 19th-century character. Public education is provided by the Mansfield Township Elementary School District for the youngest students, with older students attending the Warren Hills Regional School District's middle and high schools. The township maintains recreational facilities, including a 128-acre park off Port Murray Road, and residents draw on the surrounding region for shopping, dining, and services. State Route 57 is the township's principal roadway, connecting to the broader state highway network and, within a short drive, to Interstate 80.