Old Kilcullen, formerly Kilcullen, is a townland in County Kildare, Ireland, which includes a noted religious archaeological site within its boundary. As a townland it is relatively large but lightly populated. The location of the townland is roughly contained within the R418 and R448 routes starting at its most northerly point, a crossroads known locally as Thompson's Cross. The townland continues south from this point as far as Harklow and is intersected in its north east corner by the M9 motorway at Abbeyaun. Old Kilcullen was formerly the site of a walled town, and before that of an ecclesiastical settlement dating from the 5th century. The original settlement gave its name to the substantial surrounding civil parish and barony.

Kilcullen, formally Kilcullen Bridge, is a small town on the River Liffey in County Kildare, Ireland. Its population of 3,815 at the 2022 census made it the 13th largest settlement in County Kildare. From 2002 to 2011, it was one of the fastest growing towns in the county, doubling its population from 1,483 to 3,473. It is situated primarily in the Barony of Kilcullen, with a part in the Barony of Naas South, and subsidiary areas include Logstown, Harristown, Carnalway and Brannockstown, Gilltown, Nicholastown, and Castlemartin.