Arthur was the son of James Enos McMilan and his wife, Betsey Elizabeth Haswell. He was born 24 Sep 1831 at Franklin County, New York and died 15 Nov 1907 at Cresco, Iowa. He married Rebecca Cheevers on 2 Feb 1854 at Elgin, Illinois. She was born about 1834 at Ohio and died 7 Dec 1893 at Cresco, Iowa. She was the daughter of Peleg and Sophia (Sebring) Cheever.