What is the difference between county and state roads?

United States

You have asked a somewhat complicated question and the answer is not exactly the same in every state. Some states have counties that maintain a strong county government. The county government is carried out by one or more county commissioners. County roads are built, improved and maintained by the county highway department. County governments have been abolished in some areas and in that case control of the county roads would pass to the state administratively.

A second type of highway system in the U. S. is the state highway system of numbered roads. These roads are built, improved and maintained by the state highway department that is usually part of the state department of transportation.