Infographic map depicting US population change as a percentage between 2010 and 2020. Each coloured unit represents a US County. McKenzie County in North Dakota, with a 2020 population of just 15,242, was the fastest-growing U.S. county over the past decade. The county?檚 138% increase was driven primarily by the Bakken oil boom in the area. High-growth counties in Texas also grew as new sources of energy were extracted in rural areas. Data from US Census Bureau 2021.