County Carlow is in the south east of Ireland. The Carlow area has been settled since circa 6,000 BCE. The earliest settlers possessed the tools of their time, usually made of flint, traces of which have since been found and preserved. Carlow's early settlers built monuments around the county which still stand today, like the Browneshill Dolmen which lies 3km east of Carlow town.

The first notable event to take place in County Carlow occured in 300 BCE, when Dinn Righ, a hill fort near Leighlinbridge, was destroyed by Labraidh Loinseach, an early Celtic settler. Christianity later came to Carlow, prompting the construction of the monastery in St. Mullins, which is believed to have been built in the 7th Century. Its ruins still exist today.

The county itself is understood to have been created during the reign of King John, which lasted from 1199 to 1216 CE. This period saw the construction of Carlow Castle, which was overseen by William de Marshall. Recent excavations suggest that the construction commenced in 1210 CE and finished ten years later. It originally consisted of a hollow square, with a round tower at each corner.

However, all that remain today are its ruins. In the early 1800s, Dr. Philip Parry Price Middleton spent £2000 attempting the turn the building into a lunatic asylum. As part of the modifications to the building, an underground passageway was to be created using dynamite. On 13 February 1814, the explosion took place with disastrous effects, with the blast bringing down the eastern wall, the east towers and the adjoining walls.

One of the earlier events of note to take place in the region occured in 1394. With Ireland under British rule, King Richard II's cousin, Roger Mortimer, was killed by the forces of Borris native Art McMurrough Kavanagh, King of Leinster. This took place in Kellistown, near Tullow, shortly after Richard II had departed the region with a 10,000-strong force, having signed a treaty with a view of ending attacks on Norman forces. The enraged monarch returned to defeat Kavanagh, but the venture ended in disaster and defeat for the King's forces. The kingdom was returned to the King of Leinster, and Carlow became a Gaelic dominion.

In 1798, a large scale uprising took place against British forces took place, led by a revolutionary group known as the United Irishmen. By the time the rebellion began, there were 11,000 members of the group in the county. On 25 May, 2,000 rebels descended on Carlow town, however the town's defenders had received word of the rebels plans in advance, and set out to give them some leeway so that they would advance quicker than expected and become disorganised. Tragically for the rebels, this worked to perfection. With the United Irishmen now expecting an easy victory, they were under little order as they reached Tullow Street and Potato Market. Celebratory cheering, known as 'the roar of a thousand voices' provided the cue to those inside the buildings and on the rooftops to open fire. The result was a convincing and a complete victory for the defenders who are understood to have suffered no fatalities. The bodies of 640 United Irishmen were thrown together in a pit, locally known today as the Croppies Grave, which can be visited in Graiguecullen.

In 1820, natural philosopher John Tyndall was born in Leighlinbridge, whose experiments included elucidating the blue of the sky.

In 1844, Carlow's workhouse was built with a capacity of 800 people. It was to be put to use in the years that followed, to accomodate those suffering from the nationwide 'Great Famine'. In September 1845, during a period of high unemployment, the first signs of potato crop failure appeared in County Carlow. Within six months, few potatoes from that years crop remained, and the government established relief schemes to provide work. Most of the following years crop was diseased, and soup kitchens were set up across the county.

Despite the assistance Carlovians received and the fact that Carlow fared better than most counties, 11,000 died from fever, cholera and starvation. Others fled the country. In 1841, 86,000 people lived in County Carlow - almost twice the population today. Ten years later, the number of residents had decreased to 68,000.

Carlow was a grim place entering the 1900s. Unemployment was rife, and the population was generally quite poor. In 1926, much needed investment was provided, when Edward Duggan succeeded in bringing Ireland's first sugar beet factory to Carlow town. The factory operated for nearly 80 years, until its closure in 2005.