Dallas County is the second-most populous county in the U.S. state of Texas with a 2020 U.S. census of 2,613,539, making it the ninth-most populous county in the country. Dallas County is included in the Dallas-Arlington-Fort Worth metropolitan statistical area—colloquially referred to as the Dallas–Fort Worth metroplex. Municipal expansion within Dallas County has blurred the geographic lines between cities and between neighboring counties.

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.