County Tyrone (Irish: Contae Thír Eoghain) is the second largest of the nine counties of Ulster and the largest of the six counties of Northern Ireland. It has an area of 3,155 square kilometres (1,218 square miles).

The county borders the Northern Ireland counties of Armagh, to the south-east, Fermanagh, to the south-west and County Londonderry to the north-east. The county also borders Lough Neagh to the east. The borders with the Republic of Ireland are County Monaghan to the south and County Donegal to the north-west.

Historically Tyrone stretched as far north as Lough Foyle, and comprised part of modern day County Londonderry east of the River Foyle. The majority of County Londonderry was carved out of Tyrone between 1610-1620 when that land went to the Guilds of London to set up profit making schemes based on natural resources located there. Tyrone was the traditional stronghold of the various O'Neill clans and families, the strongest of the Gaelic Irish families in Ulster, surviving into the seventeenth century. It is one of four historic counties of Northern Ireland to presently have a majority of the population from a Catholic community background, according to the 2001 census.