It used to be any railroad that wanted to carry US Mail, so all of them, was required to hitch at least one passenger car onto their trains. The railroad executives insisted that this was so burdensome it would put them out of business so the law was changed. But before that change you could take a train to literally anywhere in the USA where freight trains go, which is basically everywhere including many small towns.

E.B. White wrote a marvelous essay on the subject called The Railroad.