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 was the hometown of Bryant H. Womack, recipient of the Medal of Honor for actions during the Korean War.The Rev. Joshua D. Jones House was added to the National Register of Historic Places in 1991.The Tryon International Equestrian Center, near Mill Spring, will be the location of the 2018 FEI World Equestrian Games.