Around 4,500 B.C. the first farmers arrived at the Burren in county Cavan. They cleared forestry and created settlements where they lived, worshiped, and died. Remains of these settlements are evident from the magnificent archaeological monuments like the Giant’s Grave wedge tomb.

O'Reilly (Irish: Ó Raghallaigh) is a group of families, ultimately all of Irish Gaelic origin, who were historically the kings of East Bréifne in what is today, County Cavan. The kingdom lasted from 1256 to 1607.

The Plantation of Ulster from 1610 saw the settlement and origins of several new towns within the county. Wars during the mid-seventeenth century aimed at trying to unsettle the Plantation only led to further plantations of English and Scottish settlers into the county and the beginnings the flax and linen industry.

Some areas of Cavan were hard hit by the Great Famine/Hunger between 1845–49. Several instances of eviction also occurred during the nineteenth century, with one such story where the local landlord in Mountnugent parish decided to evict over 200 people. The famous ballad "By Lough Sheelin Side" is based on this event witnessed by the local Catholic priest.

In 1867 John Boyle O’Reilly was transported to Australia for his activities as a Fenian. In 1869 he escaped and ended up in Boston. In 1875 he assisted Clan na Gael in a plan to free six leading Fenians from captivity in Australia. The Catalpa departed from New Bedford in 1875 and landed back in New York with the Fenians on board in 1876.

Famous people from Cavan include, John Boyle O’Reilly, Saint Dallán, Francis Sheehy Skeffington, Marcus Daly , Cathal Buí Mac Giolla Ghunna, Alejandro O'Reilly, Thomas McGovern, Agnes O'Farrelly, Patrick O'Rorke, and Mary Anne Sadlier.