Firm Size Data(Small Business Adm.)
"This website provides data on businesses with and without employees. These are referred to as “employer firms” and “nonemployer firms.” Employer firms have the lion’s share of receipts and payroll, while nonemployer firms are far more numerous.

The U.S. Census Bureau provides Advocacy with data on employer firm size in the Statistics of U.S. Businesses (SUSB). In these data, a firm is defined as the aggregation of all establishments owned by a parent company (within a geographic location and/or industry) that have some annual payroll. A firm may be located in one or more places..."