In 1788 Francis Bernard, afterwards the 1st Earl of Bandon, pulled down the two fronts which had been added by his predecessors, and connected the old castle by a corridor (some 90 feet in length) with a mansion he erected a little to the east of the stronghold. This new part has large rooms, the library being a very handsome oval apartment.
This forms the present beautiful country seat of the Earl of Bandon. It is situated in a park about four miles in circumference, through which the Bandon River flows.
The O’Mahonys were not a powerful sept: their regular field force only numbered twenty-six horse, no gallow-glasses, and a hundred and twenty kern.
In 1575 the O’Mahony paid his respects to Sir Henry Sidney during his visit to Cork, of whom Sir Henry writes that he was “a man of small force although a proper countrie.”
Conoher O’Mahony, of Castle Mahon, threw in his lot with the Earl of Desmond during his rebellion, in which rising he was killed at the age of twenty-three.
In 1587, an inquisition held at Cork found that Conohor O’Mahownye, late of Castle Mahown, entered into rebellion with Gerald, late Earl of Desmond, and was slain therein and that he was seized of Castle Mahown and of the barony or cantred of Kineallineaky.
The following year the castle and lands were conferred by patent on Phane Beecher, son of Alderman Henry Beecher, of London.
Mr. William Weever, in his “discourse” on the Munster rebellion of 1598, records that Mr. Beecher deserted Castle Mahon during the rising.
In 1611 it seems the grant to Phane Beecher was confirmed.
The first Bernard to settle in Ireland during Elizabeth’s reign had a son Francis, who was lord of the manor of Castle Mahon, where he lived before the rebellion in 1641. He had one son, Francis, who was in possession of the castle in 1690 when Bandon was surprised and taken by Colonel M’Carthy’s men. After the town had fallen into their hands they proceeded to Castle Mahon and demanded the fortress and its stores to be given up to King James, and the garrison to surrender as prisoners.