County Leitrim was established in 1583 when Lord Deputy Sir John Perot marked out its boundaries. The county formed part of the old Gaelic kingdom of Breffni, which was ruled by the O'Rourkes.

Large parts of the county were confiscated from its owners in 1620 and given to English landlords, including Villiers and Hamilton, who founded the town of Manorhamilton. The objective was to plant the county with English settlers, however this was largely unsuccessful.
 

Carrick on Shannon became the chief town of the county, which had one other borough, Jamestown  built for settlers in the 17th century. There were three other market towns, Manorhamilton, Ballinamore and Mohill.

The county was very badly affected by the Great Famine of 1845-47. The population was 155,000 in 1841 and by 1851 had fallen to 112,000.  It has been a high-emigration county ever since these times.  The population is currently approximately 25,000.
 

County Leitrim takes its name from the village of the same name situated close to the River Shannon. The village was an O'Rourke stronghold during the Medieval period and was a place of some strategic importance as the river nearby is comparatively shallow and narrow and therefore easily forded.

The Irish form of Leitrim - 'Liath Druim' - means the grey ridge and is a common place name in Ireland as we find over forty "Leitrims", either as townlands, villages or streets in the country.
 
There are several beautiful lakes of which the best known are Lough Gill, Lough Allen, Lough Garadice, Lough Glenade, Lough Rynn, Lough MacNean and Lough Melvin the western shores of which are in County  Leitrim. Many of the smaller lakes are also picturesque.
 

The county, in the Medieval period, was thickly forested and five great forests endured into the 17th century. The soil of Co. Leitrim is particularly water retentive and alongwith its many lakes provides the basis for the standard joke that land in the county is sold by the gallon rather than by the acre.