ANyone in Ireland know anything about the Barony of Costello?

No but if you search on the web you will find a site called rootsweb.com which gives a list of baronies in Ireland. I don't know anything about this site and it might not be accurate. It appears to be near Ballyhaunis co. mayo so you could search for info on that area also. Baronies tend to be a legacy of the British occupation of Ireland years ago and certainly are rarely if ever used or referred to in Irish life today. Only exception would be if you were buying an isolated property which might need a location description.

Costello or Costelloe is quite a common name here. It might not necessarily mean that your ancestors came from that area.

Below there are links to a Barony map of the Connacht Region showing the Costello Barony, a map showing the Dynasties and Territories of Connacht, a present day map showing the towns of that region, the Leitrim-Roscommon 1901 Census Search which lists the Townlands and Parishes of the Barony of Costello and a couple of other sites dealing with the name. I hope you find some of them useful.

hmmmmmmm

mine are from just north of Dublin I think