Joseph D. Loughrin, 74, a retired investigator with the Department of Agriculture and a former D.C. policeman, died Sunday at Georgetown University Hospital. He had Parkinson's disease.

Mr. Loughrin was born in Cadillac, Mich., and attended University of Detroit. He moved to Washington in 1932 and joined the D.C. police department. He held the rank of detective sergeant when he retired for reasons of health in 1957.

He then took a job in the office of the inspector general of the Agriculture Department, investigating possible violations of government regulations concerning the processing of meat and other foodstuffs. He retired a second time in 1968.

Mr. Loughrin, who lived in Washington, was a member of the parish of Holy Trinity Catholic Church here and a 4th degree member of the Commodore John Barry Assembly of the Knights of Columbus in Arlington. He also was a member of the Association of Retired Police of the District of Columbia.

Survivors include his wife, the former Katherine Gilbert, and one son, Michael J., both of Washington; five brothers, Eugene, of Fort Lauderdale, Fla., Robert, of Cadillac, Richard and Phillip, both of Hastings, Mich., and Francis, of Grand Rapids, Mich., and two sisters, Cloris Loughrin of Grand Rapids, and Helen Kuhn of Washington.