James Spencer Rains was born in Tennessee to Asahel and Malvina (Duncan) Rains. By 1840, Rains had moved to the vicinity of Sarcoxie, Missouri. He served as prewar general of the militia and as Newton County, Missouri judge from 1840 to 1842. In 1844, he was elected to the state house by Newton County and served in the Missouri Senate from 1854 to 1861. Between 1845 and 1852, Rains served as an agent for Indian affairs in various locations and ventured to California as a "forty-niner", where he served as a general in the California state militia. In 1860, Rains was an unsuccessful candidate for the U.S. Congress for the Southwest Missouri District. Rains County, Texas is named for his brother Emory Rains, an early Texas legislator.