This work contains every fact of importance tending to illustrate the local history of Ireland. Arranged alphabetically by place (parish, town, etc.), it provides a faithful description of all Irish localities as they existed at the time of publication (1837), showing exactly where a particular civil parish was located in relation to the nearest town or towns, the barony, county, and province in which it was situated, its principal landowners, the diocese in which it was situated

Published in London in 1837, the Dictionary marked a new and significantly higher standard in such accounts of Ireland. Apart from The Parliamentary Gazetteer of Ireland published in 1845, it has not been superseded.

Lewis relied on the information provided by local contributors and on the earlier works published such as Coote's Statistical Survey (1801), Taylor and Skinner's Maps of the Road of Ireland (1777), Pigot's Trade Directory (1824) and other sources. He also used the various parliamentary reports and in particular the census of 1831 and the education returns of the 1820s and early 1830s. Local contributors were given the proof sheets for final comment and revision. The names of places are those in use prior to the publication of the Ordnance Survey Atlas in 1838. Distances are in Irish miles (the statute is 0.62 of an Irish mile).

The dictionary gives a unique picture of Ireland before the Great Famine.

These pages cover the towns and villages and the then civil parishes of County Down.