Lacey is a city in Thurston County, Washington, United States. It is a suburb of Olympia with a population of 42,393 at the 2010 census. Lacey is located along Interstate 5 between Olympia and the Nisqually River, which marks the border with Pierce County and Joint Base Lewis–McChord.

Lacey was originally called Woodland after settlers Isaac and Catherine Wood, who claimed land there in 1853. By 1891, the town of Woodland had a large enough population to apply for a post office. The request was denied because there was already a town called Woodland on the Columbia River. The name Lacey was chosen for the new post office application, presumably after O. C. Lacey, the local Justice of the Peace. The small settlements of Woodland and Chambers Prairie consolidated into Lacey in the 1950s. The city of Lacey was not officially incorporated until 1966.