Oscar C. A. Adams was born 15 Dec 1861 to John Q. and Julia (Van Brocklin) Adams. As a young man, he left his home in Stephenson co., Illinois to join his brother Morace in farming at Grundy co., Iowa. On 24 Nov 1887, he married Mary "Lena" Seemann at Sutherland, O'Brien co., Iowa, and they lived in Iowa until 1909 when they moved to Lemmon, Perkins co., South Dakota.

On 17 Jul 1920, Lena died from heart failure while working in her garden. She was buried at Lemmon. About 1931, Oscar left South Dakota to go back to Sutherland, and in 1938 moved to Sioux City to live with his sister, Clara Younger.

He died on 25 Sep 1940 in Sioux City, Woodbury co., Iowa, at the age of 78, following a gall bladder operation. He was buried in Lemmon, Perkins co., South Dakota with his wife.

Oscar and Mary (Seemann) Adams were the parents of four children: Arthur, Elmer, Ruth and Julia, who died as an infant.