If you're looking for synonyms for the phrase "county courthouses," there are a few different options available depending on your context. One common alternative would be to refer to these buildings simply as "courthouses," without specifying that they belong to a county government. Other choices might include "county seat," "judicial center," or "legal center." In some cases, you could also use more specific terms like "superior court" or "magistrate's court" depending on the types of proceedings that take place in these buildings. Ultimately, the right synonym will depend on the particular context in which you're using the term.