Simon K. Mowry was born on October 3, 1836, in Rhode Island to Ziba Mowry and Evelina Smith. His father was a farmer and carpenter who owned $1,600 of real estate and $300 of personal property by 1860. He grew up and attended school in Greenville, Rhode Island, and by 1860, he was working as a farm laborer. He married Mary Crossman around 1870, and they had at least two children: Gilbert, born around 1871; and Charles, born around 1876. They lived in Smithfield, Rhode Island, and Mowry worked as an overseer. He died there on June 13, 1896.