- A County: Any county located in one of the 25 largest U.S. cities that have more than 20,000 households. A Counties represent highly urbanized areas and account for more than 40% of households in the United States.
- B County: Any county that does not qualify as an A County, which also has a population of at least 150,000, or is part of a consolidated statistical area with a population over 150,000. B Counties have at least 85,000 households, and when combined, account for about 30% of all U.S. households.
- C County: Any county or consolidated statistical areas that is not an A County or a B County and has a population over 40,000. A C County has more than 20,000 households, or is located in Consolidated Metropolitan Statistical Areas or Metropolitan Statistical Areas that have more than 20,000 households. C Counties account for more than 15% of the households in the United States.
- D County: Any county statistical area that is not designated as an A, B or C County (no limits placed on population). D Counties are considered very rural and are generally far from any sizable population center. When combined, D Counties account for roughly 15% of all U.S. households.