It depends on which Mercer County you are asking about. There
are eight Mercer Counties in different states across the US.
According to the NACo, the county seats for each Mercer County is
as follows:
* Mercer County, Illinois: Aledo * Mercer County, Kentucky:
Harrodsburg * Mercer County, Missouri: Princeton * Mercer County,
North Dakota: Stanton * Mercer County, New Jersey: Trenton * Mercer
County, Ohio: Celina * Mercer County, Pennsylvania: Mercer * Mercer
County, West Virginia: Princeton