ReferenceUSA is a database provided through Salt Lake County libraries that contains detailed information on over 14 million US businesses and 210 million US residents. It includes data like employee numbers, estimated sales, credit ratings, and competitor information for businesses. Library card holders can use ReferenceUSA for free to research businesses and residents. They can perform quick searches or more advanced searches using search criteria and filters. The document provides step-by-step instructions for accessing and searching ReferenceUSA through the library website or from home.