County Business Patterns provides data on the total number of establishments, mid-March employment, first quarter and annual payroll, and number of establishments by nine employment-size classes by detailed industry for all counties in the United States, the District of Columbia, and Puerto Rico. 

Employers without a fixed location within a state (or of unknown county location) are included under a "statewide" classification at the end of the county tables. This incomplete detail causes only slight understatement of county employment. The independent cities in Virginia, and the cities of Baltimore, MD; Carson City, NV; and St. Louis, MO, are treated as separate counties.