Those of us who have Trahey ancestors from Newfoundland can probably trace our line back to a Timothy Trahey born abt. 1835 in Newfoundland.No doubt that this Timothy's ancestors came to NFLD before his birth! The earliest known appearances of Trahey's in Newfoundland was 1st in a census for 1794-1795 when a Michael Trehey was recorded as owning property at Petty Harbour. Source: _ Family Names of the Island of Newfoundland_ By E.R. Seary.
Another document which I found on the Newfoundland site for the 1794-1795 census of Petty Harbour was a reference to a W. Trehey. (W. probably stands for William) This W. Trehey was a landowner in Petty Harbour whose land was occupied by an Ann Williams. It states that Ann had occupied the land for 9 years and was a widow for the same amount of time. Ann's occupation, Laundress.
Judge John Trahey said he had heard the family was in Newfoundland before the 1800's. These two documents seem to give credibility to his statement.
Next known appearance of the name is for a James Threighy (Trehy in 1806):
"11-25-1806 Anne, of William Skehan and Eliza [Elizabeth] Roberts sps. [sponsors] James Threighy [Trehy] and Mary Gushu [Gushue] 
11-25- 1806 Catherine, of Sylvester Leary and Eliza [Elizabeth] Lyons; Sps. [sponsors] Robert Connel and Idene Cole;  [It appears the Gushue's, Leary's, Skehan's, Cole's, Costello's, Driscoll's and Trehy's had all traveled to Harbour Grace from the Bacon Cove and the Kitchuses area in a group on 11-25-1806; all were from the Gaster's bay area-PFG]"
 Immaculate Conception RC Church Records, Harbour Grace, NF
This information which was dated December 30, 1996 came from the now deceased Patrick F. Gushue. His brother John gave me (as well as other Gushue descendants) all of his brother, Patrick's research on the Gushue name.
Another reference from Seary's Book of Newfoundland names includes a Thomas Trahee who was married in 1813 at Harbour Grace (Nfld. Archives HGRC);
A John Trehy with a Mary Gushue is a witness to a marriage (at the Roman Catholic Parish of St. Peter and St. Paul) between a William Keating and an Ellen Brigus on November 28, 1857. This John Trehy is probably some relation to Timothy Trahey ( Husband to Catherine Flaherty & my Mary Ann Trahey B. 1858's father). I would speculate that Johncould be Timothy's father or a brother.
Seary also records a John Trehy, farmer of Cat's Cove (now Conception Harbour) 1871 (Lovell).