Delta is a city in Keokuk County, Iowa, United States. The population was 264 at the 2020 census. According to the United States Census Bureā¦Delta is a city in Keokuk County, Iowa, United States. The population was 264 at the 2020 census. According to the United States Census Bureau, the city has a total area of 0.93 square miles, all of it land.