Egan is a city in Moody County, South Dakota, United States. The population was 241 at the 2020 census. The city has the name of a r…Egan is a city in Moody County, South Dakota, United States. The population was 241 at the 2020 census. The city has the name of a railroad employee. According to the United States Census Bureau, the city has a total area of 1.07 square miles, all land.