Collin County is located in the U.S. state of Texas. It is part of the Dallas-Fort Worth-Arlington metropolitan statistical area, and a small portion of the city of Dallas is in the county. At the 2020 United States census, the county's population is 1,064,465, making it the sixth-most populous county in Texas and the 43rd-largest county by population in the United States. Its county seat is McKinney.

Dallas is a city in the U.S. state of Texas and the most populous city in the Dallas–Fort Worth metroplex, the most populous metropolitan area in Texas and the fourth-most populous metropolitan area in the United States at 7.5 million people. It is the most populous city in and seat of Dallas County with portions extending into Collin, Denton, Kaufman, and Rockwall counties. With a 2020 census population of 1,304,379, it is the ninth-most populous city in the U.S. and the third-most populous city in Texas after Houston and San Antonio. Located in the North Texas region, the city of Dallas is the main core of the largest metropolitan area in the Southern United States and the largest inland metropolitan area in the U.S. that lacks any navigable link to the sea.