Definition:
A "county town" is a noun that refers to the main town or city in a county (a smaller area of land within a country) where the local government offices are located. It is often the administrative center for that county.
In some regions, the county town may also be a hub for commerce, education, and cultural activities. It can be a place where residents go for various services, shopping, and entertainment.
There are no specific idioms or phrasal verbs that directly relate to "county town," but you might hear phrases like "in the county" or "county lines" referring to areas within a county.