Alder is a census-designated place (CDP) in Pierce County, Washington, United States. As of the 2020 census, Alder had a population of 212.
The community is located along the shore of Alder Lake on State Route Highway 7 near the entrance to Mount Rainier National Park.
A post office called Alder was established in 1902, and remained in operation until 1975. The community was named for the alder trees near the original town site.
According to the United States Census Bureau, the CDP has a total area of 3.24 square miles (8.4 km), of which, 3.21 square miles (8.3 km) of it is land and 0.03 square miles (0.08 km) of it (0.83%) is water.