Westport originates and gets its name, in Irish, from a 16th-century castle – Cathair na Mart (meaning “the stone fort of the beeves” or “the city of the fairs”) – and surrounding settlement, belonging to the powerful local seafaring Ó Máille clan, who controlled the Clew Bay area, then known as Umaill.
The original village of Cathair na Mart existed somewhere around what is now the front (east) lawn of Westport House. It had a high street, alleys down to the river and a population of around 700. A small port also existed at the mouth of the Carrowbeg river. Roads lead from the village to the west (West Road), the south (Sandy Hill Road) and the east (Old Paddock Road). The town was moved to its present site in the 1780s by the Browne family of Westport House to make way for their gardens and was renamed Westport.
Westport is designated as a heritage town and is unusual in Ireland in that it is one of only a few planned towns in the country.The most notable feature of his town plan is the tree-lined boulevard, the Mall, built on the Carrowbeg River.
James Wyatt finished Westport House, the stately home of the Marquess of Sligo and designed its dining room. Westport House was originally built by Richard Cassels (also known as Richard Castle), the German architect, in the 1730s, near the site of the original Ó Máille Castle.
Since the late 20th century, Westport has greatly expanded with several new estates. Some of the most populous estates are Springfield, the Carrowbeg Estate, Horkans Hill, Cedar Park, Fairways, Knockranny Village and Sharkey Hill.