Alder is a census-designated place (CDP) in Pierce County, Washington, United States. The population was 227 at the 2010 census. The community is located along the shore of Alder Lake on State Route Highway 7 near the entrance to Mount Rainier National Park.
Alder is located at 46°47′16″N 122°15′58″W / 46.78778°N 122.26611°W / 46.78778; -122.26611 (46.787849, -122.26619).
According to the United States Census Bureau, the CDP has a total area of 3.24 square miles (8.4 km²), of which, 3.21 square miles (8.3 km²) of it is land and 0.03 square miles (0.08 km²) of it (0.83%) is water.