It isn’t easy to develop Irish family trees because of the loss of so many records in the fire in the Four Courts PRO back in 1922. I offer the following thoughts:
David Craig’s site was brilliant on Drung families but the link I had (
http://homepage.ntlworld.com/david.craig/craigfami/index3.htm) is no longer accessible.
I have full transcripts of the 1796 Flax Growers Lists for the Parishes of Drung and Drumgoon (ie Cootehill) but see no Cowin/Cowans.
More positively:
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearchthrows up no entries for Cowin but has 16 Cowans, including a Thomas in Drung who presumably is one of your Cowins..
In the neighbouring parish of Ashfield, the site
http://freepages.genealogy.rootsweb.ancestry.com/~adrian/Ash_Bap1.htmhas several “Cowans” (Henry 1822; Atty 1840; Mary 1842; Thomas 1845 ..) I expect that these would also be linked?
Otherwise, I’ve found that the site
http://pilot.familysearch.org/recordsearch/start.html#p=homecan be useful, but unless you have some pre-existing details (eg know the names of both parties to a marriage) or are following an unusual name, you will have to purchase a copy of each potentially relevant certificate from the Irish General Register Office. However this site does provide the references (registration district, year/quarter and page numbers) you need to order the cert, and saves a great deal of sifting through the manual records held in that Office.
http://www.census.nationalarchives.ie/gives access to the 1911 Census and our National Archives expect to have the 1901 Census up shortly. The search facility is good but requires precise spelling of entries.
I have perused the surviving records for Drung in the 1821 Census held in hard copy in the National Archives offices, but unfortunately didn’t transcribe any Cowins or Levistons.
Otherwise, personal examination of the records held by the Church Representative Body in Dublin, or where available, in the local parish, seem to be the main residual options unless you are willing to take the fee-paying route.
Taking up your kind offer to transcribe relevant items on your List, my particular interest is in the Fannin, Foster and Rountree familes.
regards
F