Fort Mill, also known as Fort Mill Township, is a town in York County, South Carolina, United States. It is a suburb of Charlotte, North Carolina. As of the 2020 census, the population of the town was 24,521. Some businesses and residents in the Indian Land community of neighboring Lancaster County share a Fort Mill mailing address, but the official town boundary extends only within York County.

The town of Fort Mill was established in 1873, getting its name from its location between two points, the first, a fort constructed by British in colonial times to protect the Catawba Indians from marauding tribes to the north, and the second point of Webb's Mill. The Catawba Indians made their home in present-day Fort Mill for many years. Scots-Irish settlers began arriving in the 1750s and 1760s and a small settlement soon developed. Fort Mill grew rapidly in the late 19th century as textile mills were established. After many textile mill shut-downs the town continued to grow rapidly and became a major suburb of Charlotte.

Highlights in Fort Mill's history include:

The Banks-Mack House, Fort Mill Downtown Historic District, Mack-Belk House, Mills House, Nation Ford Road, National Guard Armory, Spratt Cemetery, Springfield Plantation House, Thornwell-Elliott House, Unity Presbyterian Church Complex, John M. White House, William Elliott White House, and Wilson House are listed on the National Register of Historic Places.

According to the United States Census Bureau, the town has a total area of 19.97 square miles (51.7 km²), of which 19.71 square miles (51.0 km²) is land and 0.26 square miles (0.67 km²) (1.30%) is water. Interstate 77 passes through the western portions of the town, and exit 85 is signed "South Carolina Highway 160/Fort Mill." SC 160 is the main east–west street in Fort Mill.

The town of Fort Mill held a final public hearing in October 2008 on a proposed annexation that doubled the town's physical size. Fort Mill has three golf courses. The town also maintains six parks: Harris Street Park, Steele Street Park, Doby Bridge Park, Calhoun Street Park, Veterans Park and Walter Elisha Park. Three of the six parks have picnic shelters, children's playgrounds, and restrooms. Doby Bridge and Harris Street Parks have lighted baseball fields, with Steele Street and Harris Street Parks having basketball courts, and Steele Street Park having a small water park. The town also maintains a banquet hall rentable through the parks and recreation department.

Fort Mill is located in a humid subtropical climate, Cfa in the Köppen climate classification. This means that the city experiences four distinct seasons, although the variation between the seasons is not as pronounced as in other parts of the United States. Generally, daytime maximum temperatures in the summer are around 90 °F (32 °C), with nighttime low temperatures of approximately 70 °F (21 °C). In winter, daytime maxima average around 50 °F (10 °C) while nighttime low temperatures are near 30 °F (−1 °C). Occasional readings as high as 105 °F (41 °C) are seen, reaching a high of 108 °F (42 °C) in 2007 or as low as −5 °F (−21 °C) in 1989. Summers are generally humid and prone to thunderstorms, while winters are rainy with sleet and occasional snow. Snow might fall during the winter but usually does not accumulate or persist as ground cover. Fort Mill experiences rainfall related to tropical cyclones but is generally too far inland to experience damaging winds. Fort Mill has not had any direct hits from any tropical systems since 1989, when Hurricane Hugo devastated the area.

The most common soil in Fort Mill is Cecil series.