Delta is a home rule municipality that is the county seat and the most populous municipality of Delta County, Colorado, United States. The …Delta is a home rule municipality that is the county seat and the most populous municipality of Delta County, Colorado, United States. The town population was 9,035 at the 2020 United States Census. The United States Forest Service headquarters of the Grand Mesa, Gunnison, and Uncompahgre National Forests are located in Delta.