Lake Carnegie is a reservoir that straddles the borders of the towns of Princeton, West Windsor, Plainsboro and South Brunswick in Mercer and Middlesex counties in central New Jersey. The lake was created by construction of a dam along the Millstone River, though the lower portion of the lake actually follows the valley of its largest tributary, the Ston…Lake Carnegie is a reservoir that straddles the borders of the towns of Princeton, West Windsor, Plainsboro and South Brunswick in Mercer and Middlesex counties in central New Jersey. The lake was created by construction of a dam along the Millstone River, though the lower portion of the lake actually follows the valley of its largest tributary, the Stony Brook. The Delaware and Raritan Canal and its associated tow path are situated along the eastern shore of the lake. Noted businessman and philanthropist Andrew Carnegie donated money for the construction of the lake, which was donated to Princeton University. In 1990, the Lake Carnegie Historic District was listed on the National Register of Historic Places.