The Irish form of MacElderry (Often written as MacIlderry) is Mac Giolla Dorcha (dorcha, dark). It is a well known name in Co. Tyrone but now numerous in Co. Antrim The McElderry family has been prominent in and around Ballymoney for a long time. The 1825 Tithe Aplotments listed:
Thomas, Gordon Moss (A moss is a peat bog)
John, Leitrim townland
In the late 19th. C a Thomas was Chairman of the Ballymoney Town Commissioners and Thomas and John were elders of the 2nd. Ballymoney Presbyterioan Church.
The biography of Robert Knox McElderry of B'money is given in the Dictionary of Ulster Biography (Ulster History Circle). PRONI has "A short history of the Presbyterian churches of Ballymoney, 1898" which has info on the family. Many family members emigrated to Canada, the U.S. and the West Indies. The McIlderry grave numbers are 65, 119, 284 and 286 in Dorothy Arthur's, "Ballymoney Old Churchyard".
Jane or Jean McElderry, daughter of Robert, married Samuel Lamont. The name is still found in B'money through bt.com