Sunday Lake is a census-designated place (CDP) in Snohomish County, Washington, United States. As of the 2020 census, Sunday Lake had a population of 1,184.
According to the United States Census Bureau, the CDP has a total area of 1.79 square miles (4.65 km), of which, 1.73 square miles (4.48 km) is land and 0.06 square miles (0.17 km; 3.57%) is water.