The name Garret/Garrett is common in County Down as well as the Ballymacarret/Knockbreda area of Belfast. See the Ros Davies Co. Down web site under surnames. I knew of several prominent families in and around Holywood. The 1843 Belfast Directory listed:
Bernard, News vendor, Green St.
Mrs, Cromac House.( Home of Henry Garret, Solicitor)
James, House carpenter, May St.
Henry, House carpenter, College St.
Henry & James R., Solicitors, Castle Lane
William, Flesher, Hercules St.
William, Hair cutter, Church Lane
Robert, Paper & Rag Merchant, Telfair's Entry
More recent directories on the Lennon
/Wylie web site