Tonyhallagh (from Irish: Tonnaigh Shalach, meaning 'The Miry Pasture') is a townland in the civil parish of Templeport, County Cavan, Ireland. It lies in the Roman Catholic parish of Templeport and barony of Tullyhaw.
Tonyhallagh is bounded on the north by Cavanaquill townland, on the west by Lissanover townland, on the east by Crossmakelagher townland and on the south by Killycluggin townland. Tonyhallagh's chief geographical feature is pastureland.
Tonyrevan is traversed by minor roads and rural lanes.
The townland covers 38 statute acres.
The 1609 Baronial Map depicts the townland as part of Killcloggin (now the modern townland of Killycluggin).
The 1665 Down Survey map depicts it as Tonycullagh.
William Petty's 1685 map depicts it as Tonycula.
Another name for the townland was Rostonimore (from Irish: Ros Tonnaigh Mór, meaning 'The Wood of the Big Pasture')
In the Dúchas Schools' Collection, a story by Francis Maguire describes local legends about Tonyhallagh at http://www.duchas.ie/en/cbes/5044789/5038323
In the Plantation of Ulster by grant dated 27 February 1610, along with other lands, King James VI and I granted one poll of Tawnihulch containing 50 acres at an annual rent of £0-10s-8d to Cahill McBrien O'Reily, gentleman.
Cathal O'Reilly then sold the land to Walter Talbot of Ballyconnell.
An Inquisition held at Cavan Town on 14 March 1630 found that Walter Talbot died on 26 June 1625 at Ballyconnell and his son James Talbot succeeded to, inter alia, one poll in Tonenelwlagh, aged just 10 years. James Talbot married Helen Calvert, the daughter of George Calvert, 1st Baron Baltimore of Maryland, USA, in 1635 and had a son Colonel George Talbot who owned an estate in Cecil County, Maryland which he named Ballyconnell in honour of his native town in Cavan. George Talbot was appointed Surveyor-General of Maryland in 1683. In the aftermath of the Irish Rebellion of 1641 James Talbot's estate in Tonyhallagh was confiscated because he was a Catholic and he was granted an estate in 1655 at Castle Rubey, County Roscommon instead. He died in 1687.