Leitrim is bordered by the counties of Donegal to the north, Fermanagh to the north-east, Cavan to the east, Longford to the south, Roscommon to the south-west and Sligo to the west.

Leitrim has a hilly and mountainous landscape in its northwest and is relatively flat in the southeast, each separated from the other by Lough Allen in the middle of the county.

Notable lakes include: In ancient times Leitrim formed the western half of the Kingdom of Breifne.

This region was long influenced by the O'Rourke family of Dromahair, whose heraldic lion occupies the official county shield to this day.

English Deputy Sir John Perrot had ordered the legal establishment of "Leitrim County" a half-century prior, in 1565.

Long ago Ireland was covered in woodland,[8][9] and five great forests are traditionally said to have stood in Leitrim, with a 19th-century county survey stating- "a hundred years ago almost the whole country was one continued, undivided forest, so that from Drumshanbo to Drumkeeran, a distance of nine or ten miles, one could travel the whole way from tree to tree by branches".

Coal mining became prominent in the 19th century to the east of Lough Allen at Sliabh an Iarainn and also to the west in Arigna, on the Roscommon border.

Writing in 1791, the geographer Beaufort suggested the county housing population encompassed 10,026 homes with "upwards of 50,000 inhabitants", the primary agriculture being cattle production, and the growth of flax sustaining the linen industry.

[12] Leitrim was first hit by the recession caused by the mechanisation of linen weaving in the 1830s and its 155,000 residents (as of the 1841 census) were ravaged by the Great Famine and the population dropped to 112,000 by 1851.

Glencar Waterfall, 11 kilometres (7 mi) from Manorhamilton, inspired Yeats and is mentioned in his poem The Stolen Child.

Geographically, the county is almost evenly divided along north–south lines by Lough Allen, the River Shannon and Sliabh an Iarainn.