State-sponsored plantations were an instrument in the anglicisation of Irish society from the late 1550s, and the plantation in 1620 of the Gaelic O’Rourke lordship in Leitrim represents a stage in the development of plantation policy. With the exception of a valuable overview by Victor Treadwell, focusing on the involvement of the first duke of Buckingham, historians have largely neglected the Leitrim plantation. This study seeks to explore the programme for the anglicisation of native society in the area, as illustrated in the plantation instructions. Aspirations will be compared with what can be gleaned of the actual implementation of the plantation, drawing largely on the official documentation and correspondence generated by the 1622 commission of inquiry, which was established because of unease with various aspects of state performance in Ireland, including the condition of the plantations. In the case of Leitrim, such concern was amply justified. A further theme is the impact of the plantation on the native population, and especially on the smaller freeholders who were dispossessed under the plantation. Through the natives’ complaints and other material, the 1622 documentation affords rare insights into the impact of the plantation on Gaelic society. Finally, to assess the success of the plantation, the development of the settler community to 1641 will be briefly outlined.