Melvin Grigsby was an American attorney, politician, and military leader from South Dakota. A Union Army veteran of the American Civil War, Grigsby was most notable for his service as South Dakota Attorney General and an organizer and commander of the 3rd United States Volunteer Cavalry Regiment during the Spanish–American War.

The attorney general of South Dakota is the state attorney general of the U.S. state of South Dakota. The attorney general is elected by popular vote to a four-year term and holds an executive position as the state's chief legal officer. In 1992, the voters approved a constitutional amendment to limit all constitutional officers and the governor to two consecutive four-year terms.