Sunday Lake is a census-designated place (CDP) in Snohomish County, Washington, United States.

The population was 640 at the 2010 census.

According to the United States Census Bureau, the CDP has a total area of 1.79 square miles (4.65 km2), of which, 1.73 square miles (4.48 km2) is land and 0.06 square miles (0.17 km2; 3.57%) is water.