John Jay "J.J." Dewey (September 9, 1822 – April 1, 1891) was an American physician and Minnesota territorial legislator.
He was educated at Hamilton Academy and Albany Medical College in New York state.
In 1847, he moved West to the newly settled areas Wisconsin and the young settlement of Saint Paul, in what later became the Territory and State of Minnesota.
He practiced medicine there and opened the first drug store in Saint Paul settlement.
Without outbreak of the Civil War, Dewey helped organize the Minnesota 9th Infantry Regiment and was appointed its Surgeon.