One of my great-grandfathers was born in the parish of Philipstown/Daingean in Offaly, and I may be able to help. There does not appear to be a Killoran anywhere in Offaly, but on Google Earth I found a Killoran to the southeast, across the border in County Kildare (on the other side of the parish of Clonbullogue from Philipstown). It's in the parish of Rathangan (or Kildare and Rathangan). Killoran does not appear to be a townland name, but perhaps what is sometimes referred to as a "sub-townland". located within the townland of Shean. You can find more info about Shean here: https://www.townlands.ie/kildare/east-offaly/rathangan/rathangan/shean/
At that site, they also provide links to records such as the 1901 and 1911 censuses, and also Griffith's Valuations, but there appear to be no such records for Shean. Shean is located on the western outskirts of the town of Rathangan, and it's possible that it went by another name back then (maybe even Killoran). Sometimes, especially in Griffith's Valuation, a place name will be listed as a townland when it no longer is one today (that happened in another part of my family), although the locals may still use the old name and think of it as a townland.. Actually, there's a similar naming discrepancy for Philipstown/Daingean itself, as you can see if you look around at the site mentioned above. In some records it's the one name, and in others it's the other name, and the townlands are not all linked to either name. For that reason, I've found Google Earth a better way to find the location of places in Ireland, because it often includes place names not found in the official lists of townlands, and you can actually see a satellite photo of the place, and enlarge it.
I don't know whether that's the right Killoran, but If your ancestors lived in the eastern part of Daingean/Philipstown parish (as my great-grandfather's family did), that particular Killoran would not have been very far away. I don't know for certain the origin of the name Killoran, but there is a Killoran in County Galway, and its Irish form is Cill Odhráin, menaing "Oran's Church".
Interestingly, in the parish records which I've searched in Daingean, there was a Margaret Dunn who witnessed the maririage of two of my likely relatives in 1828, so we might be distantly related. In case you haven't already looked into it, the parish records for Daingean/Philipstown go back as far as 1795 for baptisms (with a gap from 1798-1819), and 1820 for marriages,so you may be able to find your Dunne ancestors there. The online records are at this link: https://registers.nli.ie/parishes/0723
The parish records for Kilbeggan in Westmeath also go pretty far back, to 1818 for both baptisms and marriages, and you can find them online here; https://registers.nli.ie/parishes/0943
