Monarch Mill is a census-designated place (CDP) in Union County, South Carolina, United States.

[6] According to the United States Census Bureau, the CDP has a total area of 5.6 square miles (15 km2), all land.

There were 862 housing units at an average density of 153.3 per square mile (59.2/km2).

24.7% of all households were made up of individuals, and 10.1% had someone living alone who was 65 years of age or older.

About 7.6% of families and 9.5% of the population were below the poverty line, including 12.7% of those under the age of 18 and 9.3% of those 65 and older.