A county seat is a city which is the capital of a county. Note that in the United Kingdom, the term county town is usually used for the same purpose. Also note that in the U.S state of Virginia, many county seats are politically not a part of the counties they serve; under Virginia law, all municipalities incorporated as cities are independent cities and are not part of any county.
County-wide politics and government are conducted here. The county courthouse and county administration are usually located in the county seat. Connecticut does not have county seats, as all government is either done at the state level or at the municipal (town or city) level.
See also: borough seat (Alaska), parish seat (Louisiana), and shire town (Vermont).