Thomas was born in 1854, in a log cabin at Lapeer, Michigan, the son of Stephen Van Rensselaer Thomas and Caroline Louisa (Lord) Thomas, who had not long before emigrated from the state of New York. Stephen Thomas was a sturdy and enterprising young farmer who fought under Burnside and Stoneman in the Civil War, and won a captaincy in the 10th Michigan Cavalry. Later he became a lawyer and attained some prominence in politics. The bracing life of early farming days offered the son a wholesome opportunity for all-round development. At eleven years he had not only become something of a naturalist and hunter, but had won great renown as a young spelling prodigy.