During the eighteenth-century political power and patronage remained in the hands of a few powerful landlords. Ten large estates covered more than half of the entire land area of County Wicklow. The largest was the Rockingham estate, centred on Coolattin, which covered almost 80,000 of the county's 500,000 acres. Lords Powerscourt, Meath, Hugo, Wicklow and Beresford and the archbishop of Dublin held massive estates of 20,000 acres or more.
During the century, the demographic characteristics of the county underwent significant change. By the end of the century Wicklow had a higher proportion of Protestants than in any non-Ulster county. The presence of substantial numbers of both denominational groups crowded into heavily populated areas led to increased sectarian tensions towards the end of the eighteenth century. Penal Laws remained in force and a rebellion eventually broke out in 1798.
The Wicklow uplands were the scene of much violence and unrest. Geography played no small part in this development as the vast expanses of the Wicklow Mountains offered an ideal hiding place for rebel troops. Though the rebellion had been quickly defeated, the Wicklow uplands provided shelter and succour to rebel troops for a number of years afterwards. Although the government had responded to the outbreak of violence in the summer of 1798 with a ruthlessness which included summary execution, floggings and imprisonment without trial, armed rebels remained ensconced in the hills of Wicklow for the next five years.
The 1798 Rebellion aimed for independence from Britain. However, it resulted in the demise of the Irish parliament and formation of a new political entity - the United Kingdom of Britain and Ireland.
Britain was engaged in a major European war at the time and had little time for domestic unrest. It was, nonetheless, considered inexpedient for armed bands of rebels to be permitted to roam freely in a part of the newly constituted United Kingdom. Hence, a new road was constructed from Dublin, southwards, through the heart of the Wicklow uplands. This road made territory, previously remote and only accessible with great difficulty, easily and quickly accessible from Dublin. Previously, all trans-mountain routes in Wicklow had followed a north-west/south-east orientation, lying along the floors and of the valleys and glens which had been excavated by ice-movements, thousands of years previously. This new road was the first and, thus far the only, north-south route constructed through the uplands.
This Military Road, a mammoth construction which ran from Rathfarnham in south County Dublin to Aghavannagh in the south of County Wicklow, and with a spur running from Glencree to Enniskerry, took nine years to complete. The project began in August 1800 and the road was opened in stages until it was finally completed in October 1809. It was constructed by government soldiers, and it was necessary to ensure that areas were free of rebels before the military could commence construction. By the end of 1801 the least challenging part of the project, the stage from Rathfarnham to Glencree, had been completed. The difficulties encountered in constructing the road are evident even from a modern ordnance survey map as the path of the road meanders and winds through the peaks rather than following a shorter and straighter route.
The road immediately opened up access to the mountains from Dublin and from east and west Wicklow. Security was a priority and barracks and police stations were constructed along the route of the road to ensure public safety and transport security . By 1834 there were a number of police stations located along a road which three decades earlier had been a haven for the remnants of United Irishmen rebels. However, despite the development of this important communications route through the mountains, little industry was available in the upland areas, which remained relatively thinly populated in comparison to the bordering areas to the east and west. The majority of the people living in the uplands lived on the periphery of the uplands with very small population densities being exhibited in the more central parts of the mountains. There were few towns and urban centres of significance with Roundwood, located on the eastern margins, and Lackan, on the western margins, being two notable exceptions. The 1841 census, the first statutory census to provide detailed townland population figures for the county, records the total population of the uplands at about 13,000 people while the entire county had a recorded population of 126,143 persons.
Censuses have generally been held every ten years in Ireland since 1821 when the first statutory census was successfully completed. The 1841 census, immediately predating the Great Famine, recorded the population of the county at a level which has not since been surpassed. After 1841 the Famine, and the emigration which commenced in its wake, resulted in a dramatic drop in population in the county. By 1891 the county population had fallen to 62,136 - less than half the level of the pre-Famine number. The proportionate fall in numbers in the upland regions of the county was even greater as marginal lands were abandoned in favour of urban habitation.