Mill Spring is an unincorporated community in Polk County, North Carolina, United States. Mill Spring is located at the junction of North Carolina Highway 9 and North Carolina Highway 108 3.7 miles northeast of Columbus. Mill Spring has a post office with ZIP code 28756. Mill Spring is named after Colonel Ambrose Mills. He founded a saw mill and post office in the community. Mill Spring was the hometown of Bryant H. Womack, recipient of the Medal of Honor for actions during the Korean War.