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 12 miles to Monroe, the Walton County seat, and west 32 miles 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 to Conyers. Georgia State Route 81 leads northeast 16 miles to Winder and south 18 miles to Covington.
According to the United States Census Bureau, Loganville has a total area of 7.4 square miles, of which
7.3 square miles is land and 0.04 square miles, or 0.60%, is water.