Plains is a city in Sumter County, Georgia, United States. As of the 2020 census, the population of the city was 573. It was the home of Jimm…Plains is a city in Sumter County, Georgia, United States. As of the 2020 census, the population of the city was 573. It was the home of Jimmy Carter and his wife Rosalynn, who were the 39th president and first lady of the United States from 1977 to 1981.