Ballymena is a town in County Antrim, Northern Ireland. It had a population of 31,205 people at the 2021 census, making it the seventh largest to…Ballymena is a town in County Antrim, Northern Ireland. It had a population of 31,205 people at the 2021 census, making it the seventh largest town in Northern Ireland by population. It is part of the Borough of Mid and East Antrim.