Thomas Dempster was born at Cliftbog, Aberdeenshire (near Turriff), to the sister of the Baron of Balquhain, according to him in his autobiography, and Thomas Dempster Laird of Muiresk, Auchterless and Killesmont, sheriff (until 1586) of Banff and Buchan. A Laird had the rank of Baron. As the Baron of Balquhain was a member of Clan Leslie, a lowland clan (as was Clan Dempster), Thomas' mother is identified with Jean Leslie. A land charter from the king of Scotland in 1592 defines or redefines the lands to be owned by Thomas and his wife Jeanne Leslie (Jean elsewhere in the charters) and inherited by his heirs Robert (2nd son), Thomas (3rd son), and George, who are called "legitimate offspring", and also John, Archibald and Charles Dempster. Girls could not inherit, so they are not listed. The oldest son, James, is missing from the record.