The name Mill Hill refers to central New Jersey's first industrial site, a mill, erected in 1679, at the southeast corner of the present Broad Street crossing of the Assunpink Creek. Mill Hill and its wooden mill were among the holdings of the first settler in the vicinity of Trenton, Mahlon Stacy, a Quaker who arrived in North America in 1678. The mill was destroyed in a flood.
Mill Hill became famous in the late 18th century for being the site of the Second Battle of Trenton, a battle many historians consider the turning point in the American Revolutionary War. The battle took place on January 2, 1777, in what is now Mill Hill Park. Every year, this battle is re-enacted during Patriots Week in Trenton. Mill Hill remained relatively undeveloped during the first decades of the 19th century. During this time it was not yet part of the City of Trenton. In 1840, the entire area was incorporated as South Trenton and then into the City of Trenton in 1851. The name Mill Hill was applied to the area at least as early as 1821.