Mill Creek is a city in Snohomish County, Washington, United States. It is located approximately 20 miles north-northeast of downtown Seattle and is part of the Seattle metropolitan area. The 2010 census population as of 18,244. Mill Creek was originally a planned community built around a golf course and country club as its centerpiece. Based on per capita income, Mill Creek ranks 55th of 614 areas in the state of Washington to be ranked.