Firms vs. Establishments


I am currently working on a project where I am trying to measure the number of businesses in a certain city/ county. On the American FactFinder website, the Survey of Business Owners and the Business Patterns data seem to have what I am looking for, although I am confused about some of the terminology used in these datasets. The former talks about the number of firms with or without employees, whereas the latter just mentions establishments. I was wondering if someone could explain the difference between a firm and an establishment in these cases, and perhaps also give a few examples where a firm might not count as an establishment and vice versa.