Hello there!
I was delighted to see your post - I've been searching for you (or anyone in your lineage) for about five years! Camlin House, located just south of Boyle, Co. Roscommon, was one of the Irwin estates and the house still stands. If you go to Google Earth and go to the following coordinates, you can see it for yourself: 53 degrees, 54' 29.24"W and 8 degrees, 18' 27.66"W. If you type Boyle, Co. Roscommon, Ireland into the Google Earth search box and hit "enter", you will find yourself starting out north of Camlin. Look south and you will see two lakes close together just a little east of the direct line south from Boyle. Now look south-southwest and you will see a small lake that looks like the hull of a boat. Look west of that lake (Treanamarly Lough), and you will see a small river that heads west from the narrow tip of the boat shape. Simply follow that river west and you will see a house that casts a north-facing shadow. That is Camlin House! There is a village named Camlin as well, just a little southeast of the estate. The townland is also called Camlin, the civil parish is Estersnow, in the Barony of Boyle. Any reference to the Irwin estate would probably call it Camlin House, not merely Camlin.
My interest in Camlin House stems from a family mystery I've been trying to unravel for many years. It seems that my gggGrandfather, John McWilliam, may have been an employee of John Irwin from around 1840 to 1863, when all of the family except my ggGrandfather immigrated to New Zealand. John and his wife Rebecca apparently lived at the gatehouse at Camlin, although there is no sign of a gatehouse any more.
You may email me off the board if you'd like. I have a few more details about Camlin House, but not much. I would be most interested in collaborating on research into your Irwins in case anything turns up about the estate and its employees. My email address is darwinsmomATrogersDOTcom. I hope this at least helps you to see where your people came from.