John H. McCullagh (1842 – March 6, 1893) was an American law enforcement officer and police captain in the New York City Police Department. Popularly known as "Farmer John", he was a protégé of Captains Jeremiah Petty and George W. Walling and battled such notorious gangs and river pirates such as the Tub of Blood Bunch, the Battle Row and Hell's Kitchen Gangs.