James H. Slater (December 28, 1826 - January 28, 1899) was a United States Representative and Senator from Oregon. Born near Springfield, Illinois, he attended the common schools, moved to California in 1849, and settled in Corvallis, Oregon in 1850. He studied law, was admitted to the bar in 1854, was clerk of the district court of the Territory of Oregon for Benton County from 1853 to 1856. He was a member of the Territorial assembly in 1857-1858 and was a member of the Oregon House of Representatives in 1859.
Slater published the Oregon Weekly Union at Corvallis from 1859 to 1861, was district attorney for the fifth judicial district of Oregon in 1868, and a presidential elector on the Democratic ticket in 1868. He was elected as a Democrat to the Forty-second Congress (March 4, 1871-March 3, 1873) and was elected to the U.S. Senate and served from March 4, 1879, to March 3, 1885. He resumed the practice of law in La Grande, Oregon and was a member of the State railroad commission from 1889 to 1891. He died in La Grande in 1899; interment was in Masonic Cemetery.