CASTLEBAR, a town of Ireland, the capital of the county of Mayo, situated on the river of the same name, 159 miles west by north of Dublin. It consists chiefly of a main street upwards of half a mile in length and a square in which are the county courts and public offices. It also possesses a jail, an Episcopal church, a Roman Catholic chapel, a lunatic asylum, a county infirmary, a linen hall, artillery and infantry barracks, aud a workhouse. There are some breweries, and a considerable trade in linens and agricultural produce. Two newspapers are published in the town. The castle, which gives its name to the town, was a fortress of the De Burgh family; but the town itself is of more modem origin. In 1641 the castle was held for the Parliament by Sir Henry Bingham, but he was forced to surrender to Lord Mayo, and fell a victim, with all his garrison, to the fury and treachery of the besiegers. The massacre was afterwards avenged, in 1653, by the execution of Sir Theobald Burke (by that time Lord Mayo), who had been in command along with his father at the siege. In 1798 the town was occupied for some weeks by the French under General Humbert, who had defeated the English under Luke J. Hutchison in a conflict which is jocularly styled the “Castlebar Races.” Population in 1871, 3508.