Thomas King is listed in the Griffiths Valuation listing for Kilmacow civil parish from around 1850 living in Granny townland as you indicated. I searched for a marriage record for Thomas and Mary on the subscription site Roots Ireland but did not find a record. The only record of interest was a Novermber 1 1839 baptismal record for a Mary King with father Thomas King and mother Mary Donovan. The record was in the Templeorum RC parish records. Templeorum is to the northwest of Kilmacow.
Do you have any other info on the family? Were there other children?