Gideon C. Moody (October 16, 1832 - March 17, 1904) was a United States Senator from South Dakota. Born in Cortland, New York, he attended the common schools and pursued an academic course. He studied law in Syracuse, New York and in 1852 moved to Indiana, gaining admission to the bar in 1853. He was appointed prosecuting attorney for Floyd County, Indiana in 1854. He was a member of the Indiana House of Representatives in 1861, and during the Civil War entered the Union Army as a captain in April 1861 and served as captain, lieutenant colonel, and colonel, until his resignation in March 1864. He moved to the Territory of Dakota in 1864 and was a member of the Territorial house of representatives in 1867-1868, 1868-1869 and 1874-1875, serving as speaker 1868-1869, 1874-1875. From 1878 to 1883, he was an associate justice of the Territory's supreme court and was a member of the constitutional conventions of South Dakota in 1883 and 1885.
Upon the admission of South Dakota as a State into the Union, Gideon Moody was elected as a Republican to the U.S. Senate and served from November 2, 1889, to March 3, 1891. He was an unsuccessful candidate for reelection; in 1904, he died in Los Angeles. Interment was in Rosedale Cemetery.