David Palmer Knowlton was a resident of Mansfield on November 4, 1862 when he enlisted as a Private in Co. I of the 5th Regiment Connecticut Volunteer Infantry. He was transferred to Co. B, 20th Regiment of the Veterans Reserve Corps on December 12, 1863; he was discharged on July 20, 1865.

He was born November 16, 1833 in Ashford to Palmer A. and Harriet E. (Conant) Knowlton. In the 1860 U.S. census in Mansfield, he was a 26 year old farmer and head of household. David Knowlton married Elmira J. Simons/Simonds on February 28, 1853 in Mansfield. Children include: Adelaide Knowlton, born September 5, 1855; John E. Knowlton, born April 22, 1862 and Edith C. Knowlton, born January 22, 1867. His wife, Elmira died on March 18, 1867, less than two months after the birth of Edith. David Knowlton was a farmer. 

On July 17, 1866, he applied for an invalid pension, No. 112,014 but he died before it was granted. A guardianship pension application was filed under certificate No. 111,006 on October 27, 1869 that was granted under 144,258. According to the list of pensioners on the roll in 1883, the minors of David P. Knowlton were receiving a pension of $10 per month.

David P. Knowlton died of consumption in Mansfield on July 17, 1869; he is buried at the Gurleyville Cemetery in Mansfield.