list of trucking company in USA

There are a ton of transportation companies in the U.S. I really doubt there is an exhaustive list of domestic trucking companies.
If you are looking for a number of companies operating, I would think you could get an approximate number from a Google search.
If you are looking for a job, then you don't have a need to know every company. Just look through classifieds, Craig's list, Google, trucking job forums, etc.
I would think the only place to find what you want would be the DOT. But I don't think they know for certain which companies are active.

 

Transport Topics does Top 100 lists based on size. Other than that you can search http://safersys.org/