sentences:  The Yukon–Koyukuk Census Area, Alaska, is both the most extensive and the least densely populated county or county-equivalent with 0.0380 persons per square mile (0.0147/km2) in 2015.In the 50 states (plus District of Columbia), a total of 981 counties have a population over 50,000; 592 counties have a population over 100,000; 137 counties have a population over 500,000; 45 counties have a population over 1,000,000; and 14 counties have a population over 2,000,000.At the other extreme, 35 counties have a population under 1,000; 307 counties have a population under 5,000; 709 counties have a population under 10,000; and 1,492 counties have a population between 10,000 and 50,000.