Wentworth apparently intended to put down roots in Ireland: in the late 1630s he was much occupied with building a mansion, Jigginstown Castle, near Naas, County Kildare. He is thought to have intended it to be his official residence where he could entertain the King, should he visit Ireland. The castle, which was to be built partly of red brick and partly of Kilkenny marble, would, had it been completed, have been probably the largest private house in Ireland, but after Wentworth's death it quickly fell into ruin, although the ground floor still exists.