Alexandria was formed by Royal charter on March 5, 1765, from portions of Bethlehem Township, and was incorporated as one of New Jersey's initial 104 townships by an act of the New Jersey Legislature on February 21, 1798. Portions of the township were taken to form Frenchtown (April 4, 1867), Holland Township (April 13, 1874, restored to Alexandria on March 4, 1878, and recreated on March 11, 1879) and Milford (April 15, 1911). The township was named for James Alexander, a surveyor who served as New Jersey Attorney General and who had acquired of land in the area in 1744.