Katy is a city in the U.S. state of Texas. It is in the Greater Katy area, itself forming the western part of the Greater Houston metropolitan area. Homes and businesses may have Katy postal addresses without being in the City of Katy. The city of Katy is approximately centered at the tripoint of Harris, Fort Bend, and Waller counties. Katy had a population of 21,894 at the 2020 U.S. census, up from 14,102 in 2010.