Freeman T. Knowlton was born around 1835 in New York to Thomas and Louisiana Knowlton. His father was a farmer who owned $2,500 of real estate and $200 of personal property by 1860. The family moved to Whitewater, Wisconsin, in the 1850s, and by 1860, Knowlton was working as a laborer.
He enlisted in the Union army on July 15, 1862, and he mustered in as a corporal in Company D of the 20th Wisconsin Infantry. The regiment took part in the siege of Vicksburg. He eventually earned a promotion to sergeant, and he mustered out on July 14, 1865.
He returned to Whitewater after the war, and he married Jennie C. King on October 2, 1865. They had at least three children: George, born around 1872; Bertie, born around 1873; and Franklin, born around 1875. They lived in Janesville, Wisconsin, and Knowlton worked as a moulder. He applied for a federal pension in December 1879 and eventually received one. He moved to Rockford, Illinois, in the late 1800s, and he died there on September 8, 1894.