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.

Another, much older, historic site, Dun Ailinne, is located approximately one kilometre away to the north at Knockaulin.

At ground level today, the site appears to be confined to a churchyard with surviving stone features at the top of a gently sloping hill, but aerial and ground surveys have shown a far greater extent to the former settlement, including embankments on the slopes of the hill.

and JJ Kavanagh Ltd. Kilcullen began as a monastic settlement, in the period around 448, and is believed to have been assigned clergy by St. Patrick.

The settlement was assigned a bishop, (St.) Iserninus or Isernine, together with (St.) (Eoghan) MacTail or Mactalius, who later took sole responsibility.

Originally, as shown on maps even as recently as the late 18th century, the new settlement was wholly on the eastern bank of the River Liffey.

The fortification here was initially held by the parliamentary forces in 1641, but later taken by the Royalist army, and then recaptured and burned by the parliamentarians in 1647.

As a mark of respect for their Irish hosts[14] the English Napier cars were painted shamrock green.

In addition to the historic area, the townland of Old Kilcullen includes homes, farms, a public house, and a Kildare County Council reservoir.

The round tower is now just over 10m high at the lowest point of its uneven top remaining course, stabilised after damage during the Battle of Kilcullen.