Major William Cadogan (1601–1661), of Liscarton,
County Meath, was born at
Dunster,
Somerset, to Henry Cadogan of Llanbetter,
Pembrokeshire. His great-grandfather, Thomas Cadogan, of Dunster, claimed descent from the ancient princes of Wales (called Cadwgan). He was the father of the Dublin barrister
Henry Cadogan and the grandfather of
William Cadogan, 1st Earl Cadogan