Southside is an unincorporated community in Montgomery County, Tennessee, United States. Southside is located in the southeast corner of the county, 11.5 miles (18.5 km) south-southeast of Clarksville. Southside had a post office until it closed on October 12, 2002; it still has its own ZIP code, 37171. Historic Collinsville, a living museum of 19th century life, is located near Southside. The Lafayette Furnace, which is listed on the National Register of Historic Places, is also near the community.