Castletown (Irish: Baile an Chaisleáin) is a small village and also a parish in County Laois in Ireland.

The older Irish name for the town was Baile Chaisleáin Ua bhFoirchealláin (meaning "castle-town of Uí Fhoirchealláin").

[2] According to an extract from A Topographical Dictionary of Ireland, published in 1837 by Samuel Lewis, Castletown was then "a village in the Parish of Offerlane, barony of Upper Ossory, Queen’s county, and province of Leinster, 13⁄4 miles (S.by W.) from Mountrath; containing 367 inhabitants.

It takes its name from an ancient castle, occupying a commanding situation on the bank of the River Nore, and which, in the early part of the 16th century, was garrisoned by Sir Oliver Norris, son-in-law of the Earl of Ormonde, with a view to curb the power of the Fitzpatricks, to whom it was afterwards relinquished".

The extract continues “the village is pleasantly situated on the river Nore, and on the road from Dublin to Limerick, it contains 59 houses, many of which are good residences, and the whole has an appearance of neatness and respectability”.