Bloomsbury is a borough in Hunterdon County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 870,^[7][8][9] reflecting a decline of 16 (-1.8%) from the 886 counted in the 2000 Census, which had in turn declined by 4 (-0.4%) from the 890 counted in the 1990 Census.^[18]

Bloomsbury was incorporated as a borough by an act of the New Jersey Legislature on March 30, 1905, from portions of Bethlehem Township.^[19]

^

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 masses of wrought iron that are known as "blooms".