Olathe is a city in, and is the county seat of, Johnson County, Kansas, United States. Located in northeastern Kansas, it is also the fourth most populous city in the state, with a population of 125,872 recorded by the 2010 census. Olathe is also the fourth-largest city in the Kansas City metropolitan area. It is bordered by the cities of Lenexa to the north, Overland Park to the east, De Soto to the northwest, and Gardner to the southwest.