Sioux Kingsbury Grigsby (December 25, 1873 – August 21, 1968) was an attorney and politician in the United States state of South Dakota. Grigsby was born into a prominent pioneering family, Kingsbury family in South Dakota and set up a law practice which he would maintain for over 60 years. Grigsby served as state representative, state senator, US District Attorney for Alaska, Attorney General of South Dakota, and finally Lieutenant Governor of South Dakota from 1945 to 1949.