Table 1.

Definition of RUCC and population sizes for counties in the United States

kPopulation in SEERaPopulation in U.S.a
RUCCDefinitioncountiesn (%)n (%)
1Counties in metro areas of 1 million population or more47254,360,203 (62.7%)170,707,445 (54.8%)
2Counties in metro areas of 250,000 to 1 million population39517,963,604 (20.7%)66,226,176 (21.2%)
3Counties in metro areas of fewer than 250,000 population3696,104,298 (7.0%)28,501,828 (9.1%)
4Urban population of 20,000 or more, adjacent to a metro area2171,845,954 (2.1%)13,544,583 (4.3%)
5Urban population of 20,000 or more, not adjacent to a metro area921,374,217 (1.6%)4,976,874 (1.6%)
6Urban population of 2,500 to 19,999, adjacent to a metro area5972,427,381 (2.8%)14,747,534 (4.7%)
7Urban population of 2,500 to 19,999, not adjacent to a metro area4341,736,695 (2.0%)8,243,858 (2.6%)
8Completely rural or less than 2,500 urban population, adjacent to a metro area220415,639 (0.5%)2,146,218 (0.7%)
9Completely rural or less than 2,500 urban population, not adjacent to a metro area425492,659 (0.6%)2,595,449 (0.8%)
1–3Metropolitan1,23678,428,104 (90.4%)265,435,449 (85.2%)
4–9Nonmetropolitan1,9858,292,544 (9.6%)46,254,517 (14.8%)
  • aAverage population across 2009–2013.