PHILIPSTOWN, a market and post-town (formerly the assize town of the county and a parliamentary borough), in the parish of KILLADERRY, barony of LOWER PHILIPSTOWN, KING'S county, and province of LEINSTER, 7 miles (S. E.) from Tullamore, and 47 (S. W.) from Dublin; containing 1454 inhabitants.

This place, the ancient name of which was Dingan and Killaderry, was the chief seat of the O'Conors, chieftains of the surrounding district, then called Offaly, of which they retained possession until the year 1546, when Brian O'Conor having united his forces with Patrick O'More, chieftain of the neighbouring territory of Leix, made an incursion into the county of Kildare and burned a great part of Athy, whereupon Sir Wm. Brabazon, then Lord-Justice of Ireland, caused them to be proclaimed as traitors, marched a large force into Offaly, which he laid waste with fire and sword, and forced O'Conor to take refuge in Connaught. Sir William then, to secure his newly acquired possessions, erected a castle here, the name of which, in the subsequent reign of Philip and Mary, when the territories of Offaly and Leix were reduced to shire ground under the names of the King's and Queen's counties, was changed from Dingan to Philipstown, in honour of the king, and the place made the assize town of the former of these counties.

In 1569, it obtained a charter of incorporation from Elizabeth, which conferred the same liberties and free usages as the town of Naas enjoyed; also a Thursday market and other minor privileges; this charter was followed by a grant of lands in the next year. In 1673, Chief-Justice Bysse obtained for it a licence to hold two fairs. Another charter granted to it in the 4th year of Jas. II., conferred on it the privilege of returning two members to parliament.

Afterwards, during the war of that period, it was burned by the same king's troops. At the Union it was deprived of the right of returning representatives, in consequence of which the borough gradually declined, until at length the corporate jurisdiction fell into total desuetude. The act of the 2nd and 3rd of Wm. IV., by which the assizes have been removed from Philipstown to Tullamore, has completely extinguished its political importance and reduced it nearly to the rank of a village.

The town has little to recommend it. In size and population it is small, and its situation, being nearly surrounded by bog, is extremely uninteresting. Its public buildings are a court-house, formerly the county court, but now used only for holding sessions; a prison, until lately the county gaol, erected at the commencement of the present century; a large cavalry barrack, containing accommodations for 12 officers, 131 non-commissioned officers and privates, and 82 horses, with an hospital for 16 patients; the church, a neat small building; and a large and handsome R. C. chapel.

The town is paved at the expense of the county, but it is not lighted. The market, which continues to be held on Thursday, is large and improving. Fairs are held on Jan. 3rd, March 18th, May 15th, June 14th, Aug. l7th, Oct. 18th, and Dec. 3rd: four of these, termed the new fairs, from having been instituted about the year 1820, are held in a part of the town called Molesworth-street, so named from Viscount Molesworth, of whose estate the town formerly formed a part. Quarter sessions are held here four times in the year and petty sessions every second Thursday: the magisterial duties within the borough have been performed by the county justices for a series of years beyond the memory of man. A large dispensary is supported in the usual manner.

The Grand Canal passes close to one end of the town. During the progress of that work, the line terminated for some time at Philipstown and produced a sensible effect on the growth of its prosperity; but when the canal had been extended to Tullamore, that place drew to it all those advantages, and Philipstown sank still lower in trading importance.

Here is a school for boys, under the superintendence of the trustees of Erasmus Smith's charity; and there are two other public schools. The ruins of the old castle are still to be seen covered with ivy. Philipstown gives the inferior title of Baron to Viscount Molesworth.--See KILLADERRY.