The city of Limerick was founded by the Vikings in the ninth century, because of its strategic position in controlling access to the Shannon waterways, and became the capital of the Norse kingdom of Limerick. Two hundred years later, the Vikings were expelled by Brian Ború, who made it the centre of the Gaelic territory of Thomond. The county at this time was divided between Thomond and the other Munster kingdom of Desmond. After the Norman invasion in the twelfth century, it was granted by King John to William de Burgh, who erected the massive fortifications now known as King John' s Castle. The Treaty of Limerick (1691) ended Irish resistance to William of Orange, and began the wholesale emigration of the Gaelic aristocracy and minor gentry to serve in the armies of the Catholic monarchs of Europe.
The connection between the county and the verse form which shares its name is unclear. It has been suggested that it comes via an eighteenth-century Irish soldiers' drinking song, "Will you come up to Limerick", to which variously scabrous or suggestive verses were improvised.
Surnames associated with the county include Sheehan, O'Shaughnessy, O'Meara, Madigan. Woulfe, Cooke, Danaher, O'Grady, Hurley, Hogan, Noonan and O'Connor.