Question: Lifford Bridge, is a cross-border bridge on the A38 connecting with the N15, spanning the River Foyle which marks the border between Strabane, a town in West Tyrone, Northern Ireland, in which county?

Context paragraphs:
A38 road (Northern Ireland): The A38 links Strabane, County Tyrone and the A5 through the meadows of the river Foyle and over Lifford Bridge to Lifford, the County Town of County Donegal, where it links into the N14 and the N15.  The N15, which continues into County Donegal to Stranorlar, Donegal Town, Ballyshannon, Bundoran and then leaving County Donegal, before heading to Sligo.  The N14, which continues through Rossgeir, Drumbeg to Letterkenny.

Strabane: Strabane ( ; from Irish: "An Srath Bán" , meaning "the white strath" ), historically spelt Straban, is a town in West Tyrone, Northern Ireland.  It was the headquarters of the former Strabane District Council.

River Mourne: The River Mourne (Irish: "An Mughdhorn" ) is a river in County Tyrone (between Strabane and Newtownstewart), Northern Ireland, and is a tributary of the River Foyle.  At Strabane it joins with the River Finn to form the River Foyle.  Fishing is largely for salmon, grilse and sea trout.

N14 road (Ireland): The N14 road is a national primary road in Ireland.  The entirety of the route is located in the northwest of Ireland, in County Donegal, connecting Manorcunningham (approx. 10 kilometers outside of Letterkenny in the centre of the county) to Lifford in the east.  Here it connects to the N15 near the border with Northern Ireland and along the A38 to Strabane in County Tyrone.

River Finn (County Donegal): The River Finn (Irish: "Abhainn na Finne" ) is a river that flows through County Donegal in the Republic of Ireland and County Tyrone in Northern Ireland.  It rises in Lough Finn in County Donegal and flows east through a deep mountain valley to Ballybofey and Stranorlar (on opposite sides of the river) and on to the confluence with the River Mourne at Lifford.  From Castlefin downstream the river is tidal, becoming deeper towards Strabane.  The Finn is 40 mi long and together with its tributary the Reelin River, drains a catchment area of 195 square miles.  The River Foyle is formed by the confluence of the River Mourne and the River Finn, west of Lifford Bridge.  The area which the River Finn flows through is called the Finn Valley.  The village of Clady, near Strabane in County Tyrone, is on the River Finn.  The football club in Ballybofey, Finn Harps, is named after the river.

Castlefin: Castlefinn (Irish: "Caisleán na Finne" , meaning "castle of the (river) Finn" ), sometimes spelt Castlefin, is a market town in the Finn Valley of County Donegal, Ireland.  The town has a population of 810(2006) and is located between Ballybofey and Lifford.  The River Finn flows by the town.  The town is located in along the main N15 national primary road, which runs from Bundoran to Lifford.  The town lies 6 miles from Lifford and 8 miles from the twin towns of Ballybofey /Stranorlar.  It has close links to the twin towns of Ballybofey/Stranorlar, Letterkenny and has strong links with West Tyrone in Northern Ireland, especially with the towns of Strabane and Castlederg.

Strabane Lifford Development Commission: Strabane Lifford Development Commission is a cross-border body in Ireland, to develop cultural and economic development ties between Strabane in County Tyrone, Northern Ireland and Lifford in County Donegal, Republic of Ireland, just across the border marked by the River Foyle.

Lifford Bridge: Lifford Bridge (in Irish "Droichead Leifear") is a cross-border bridge on the A38 connecting with the N15, spanning the River Foyle which marks the border between Strabane in County Tyrone, Northern Ireland, and Lifford in County Donegal in the Republic of Ireland.

N15 road (Ireland): The N15 road is a national primary road in Ireland.  It begins in County Sligo in the northwest of Ireland, and ends in County Donegal.  and proceeds Northeast through Donegal, connecting Sligo to Lifford.  The route finishes at Lifford.  It continues as the A38 road from the west side of Strabane, County Tyrone, UK.  It forms part of the proposed Atlantic Corridor route.

River Foyle: The River Foyle (from Irish: "an Feabhal" ) is a river in west Ulster in the northwest of the island of Ireland, which flows from the confluence of the rivers Finn and Mourne at the towns of Lifford in County Donegal, Republic of Ireland, and Strabane in County Tyrone, Northern Ireland.  From here it flows to the city of Derry, where it discharges into Lough Foyle and, ultimately, the Atlantic Ocean.  The length of the River Foyle (total) is 129 km (80ml).  The river separates part of County Donegal from parts of both County Londonderry and County Tyrone.  The district of County Donegal that borders the western bank of the River Foyle is traditionally known as the Laggan.  This district includes the villages of St. Johnston and Carrigans, both of which are nestled on the banks of the river.

Supporting paragraphs: Lifford Bridge Strabane
Answer: County Donegal