Moses Lake is a city in Grant County, Washington, United States. The population was 25,146 as of the 2020 census. Moses Lake is the largest city in Grant County. The city anchors the Moses Lake Micropolitan area, which includes all of Grant County and is part of the Moses Lake–Othello combined statistical area. Moses Lake, on which the city lies, is made up of three main arms over 18 miles long and up to one mile wide.