Williams is a city in Colusa County, California. The population was 5,643 at the time of the 2010 census, up from 3,670 at the 2000 census. Acco…Williams is a city in Colusa County, California. The population was 5,643 at the time of the 2010 census, up from 3,670 at the 2000 census. According to the United States Census Bureau, the city has a total area of 5.4 square miles, all of it land.