Thomas was born in Russell County, Virginia, in 1863. He was the third of six sons and fourth of seven children of Sarah (Price) Thomas and Thaddeus Peter Thomas, a farmer and Methodist preacher. The mother came of Virginia stock that has been traced back to the eighteenth century. The father was descended from a German immigrant who settled in Lancaster County, Pa. , in 1749. Typical of early American sociologists, William I. Thomas came from a rural Protestant background, but little is known of his early life beyond these simple facts.