"Sligo, a county of Ireland, province of Connaught, bounded E by Leitrim, S by Roscommon, SW and W by Mayo, and N by the bay of Donegal, 39 1/2 English m. long, and 37 broad. Area, 620 square m. The soil is in general fertile, but rather boggy towards the coast, and in many parts mountainous. Chief rivers, the Sligo, Bonnet, Owenmore, Unshion, Cooloney, Esky, and Moy. Lead, iron, silver, and copper ores have been discovered, and some of the mountains exhibit strong indications of coal. Pop. 127,819."
[From The New London Gazetteer (1826)]
The Irish Ancestors website (subscription) has the following types of records: State Registration of Births, Marriages & Deaths, Census returns, Land records, Church records, Genealogical Office records, Gravestone inscriptions, Directories, Newspapers, Wills, Deeds, and Occupations.
The Fianna website's pages for County Sligo provide important addresses and extensive information about online and other genealogy resources.
Roots Ireland (subscription) "offers access to a unique database of more than 20 million Irish records". Its Sligo coverage includes Baptismal/Birth Records, Marriage Records, Burial/Death Records, Census Records and Griffith's Valuation (Free Access).