Katy is a city in the U.S. state of Texas. It is 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.

First formally settled in the mid-1890s, Katy was a railroad town along the Missouri–Kansas–Texas (MKT) Railroad which ran parallel to U.S. Route 90 (today Interstate 10) into downtown Houston. Katy obtained its name when the MKT Railroad dropped its Missouri waypoint and the junction became known as the KT stop. The fertile floodplain of Buffalo Bayou, which has its source near Katy, and its tributaries made Katy and other communities in the surrounding prairie an attractive location for rice farming. Beginning in the 1960s, the rapid growth of Houston moved westward along the new Interstate 10 corridor, bringing Katy into its environs. Today, Katy lies at the center of a broader area known as Greater Katy, which has become heavily urbanized.

While largely subsumed into Greater Houston, the town of Katy is still notable for Katy Mills Mall, Katy High School's football dominance (8 state-championships), and its historic town square along the former right-of-way of the MKT railroad.