Bloomsbury is a Borough in Hunterdon County, New Jersey, United States. As of the United States 2000 Census, the borough population was 886. Bloomsbury was incorporated as a borough by an Act of the New Jersey Legislature on March 30, 1905, from portions of Bethlehem Township. The Borough of Bloomsbury was once known as "Johnson's Iron Works", owned by Robert Johnson, on the north bank of the river. The current name is derived either from the Bloom family, influential in the early history of the town, or from the iron ore processed into "blooms," masses of wrought iron.