Plano is a city in the U.S. state of Texas, where it is the largest city in Collin County. A small portion of Plano is located in Denton County. Plano is also one of the principal cities of the Dallas–Fort Worth metroplex. With a population of 285,494 at the 2020 census, it is the ninth most-populous city in Texas, and, respectively, the 73rd most populous city in the United States.