Delta County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 31,196. The county seat is Delta. Delta County was created by the Colorado legislature on February 11, 1883, out of portions of central Gunnison County. The county was named from a delta of arable land at the mouth of the Uncompahgre River, where it …Delta County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 31,196. The county seat is Delta. Delta County was created by the Colorado legislature on February 11, 1883, out of portions of central Gunnison County. The county was named from a delta of arable land at the mouth of the Uncompahgre River, where it flows into the Gunnison River.