Try searching Lexis Nexis Academic business search. The site allows you to create a list of comanies by specific criteria including industry code, size and geographic region--state, county or city.
Search the Economic Census to find out how many businesses are operating in the US, a State, a City, or County.
Provides a detailed portrait of the nation's economy once every five years, from the national to the local level. Includes key industrial statistics such as the number of establishments, number of employees, payroll, and measure of output.
Search Google Maps to find the number of businesses operating (such as restaurants, grocery stores, copy shops) in a region.
Search Simply Analytics to find the number of businesses operating in a State, County, Census Block or Zip code. Access to consumer behavior information, such as how many households have purchased a Honda vehicle in 2008, is also available.
Search the US Small Business Administration's SizeUp to benchmark your business, map your competition, and find the best places to advertise.