Thomas Ponsonby (1660–1717) was an Irish army captain, landowner and landlord of the Crotta (historically also Crotto) estate in County Kerry.
He was the second son of Rose (née Weldon) of Athy, Kildare and Henry Ponsonby, an adventurer soldier from Cumbria in Oliver Cromwell's army which landed at Dublin in 1649.
Henry Ponsonby was confirmed in 1666 as being the new landowner of townlands confiscated from Catholics of Norman descent, largely from the Stack family; he died in 1681.
After several hearings, the court ruled in the Ponsonby's favour, a judgement challenged by Crosbie's son David, but costs drove a settlement for division of properties made after arbitration.
The list of names including Ponsonby and his father was printed in The State of the Protestants of Ireland under the late King James's Government, originally by Robert Clavell in London, and 28 years later in a book published in Dublin.