Lake Ketchum is located at (48.284778, -122.342511)
According to the United States Census Bureau, the CDP has a total area of 3.1 square miles (8.1 km²), of which, 3.1 square miles (8.1 km²) of it is land and 0.04 square miles (0.1 km²) of it (0.96%) is water.