Loganville is in western Walton County, with the city limits extending west into southeastern Gwinnett County. U.S. Route 78 (Atlanta Highway) passes through the center of town, leading east 5 miles (8.0 km) to Monroe, the Walton County seat, and west 32 miles (51 km) to downtown Atlanta. Georgia State Route 20 leads northwest from Loganville 10 miles (16 km) to Lawrenceville, the Gwinnett County seat, and southwest 15 miles (24 km) to Conyers. Georgia State Route 81 leads northeast 16 miles (26 km) to Winder and south 18 miles (29 km) to Covington.
According to the United States Census Bureau, Loganville has a total area of 7.4 square miles (19.1 km2), of which 7.3 square miles (19.0 km2) is land and 0.04 square miles (0.1 km2), or 0.60%, is water.