At the time of the defeat of the Gaelic rebellion led by Fiach McHugh in 1597, the Wicklow uplands were part of County Dublin. The area was remote and ungovernable, so the government decided to create a new county (shire), in order to bring it under more control. Two new counties were established in 1597. County Wicklow ran from Arklow to Delgany, and County Ferns was the northern part of Wexford.
The county boundaries were again redrawn in 1606 creating the County Wicklow we know today. This was the last Irish county to be formed and included Bray, Delgany, Powerscourt and Kilmacanoge in the north-east (previously part of County Dublin). Large tracts of lands were taken from the Gaelic clans and granted to English settlers. Nonetheless, Gaelic families maintained significant influence in the county in the early decades of the seventeenth century and even represented the county in parliament.
Between 1600 and 1640, the New English settlers sought to expand their estates throughout the country at the expense of Irish and Old English occupiers. Sir Thomas Wentworth, in particular, bought 34,000 acres of disputed lands in Counties Kildare and Wicklow. In 1641, rebellion broke out again. Initial successes followed, including an attack on Black Castle, located on a rocky promontory to the east of Wicklow town, by O'Byrnes in 1642.
During the war, the government borrowed money from private investors, called 'Adventurers', who were guaranteed Irish possessions following the defeat of the rebellion. There was also a belief that the only way to prevent Irish rebellions was to establish more extensive plantations throughout the country. Thus, when the war ended in 1652, an Act of Settlement was passed to remove lands from the Gaelic lords. The O'Byrnes and O'Tooles were dispossessed of their final land-holdings in Wicklow.
Ultimately, dispossessed landholders were to be transplanted to Connaught. To facilitate the operation of the Act, a detailed survey of the dispossessed lands were required. This was known as the Down Survey because the data was set down in map-form.