Kate,
I feel your pain. My grandfather's family was much smaller, but the 5 children were born in 4 different locations. It took me quite awhile to find his birth record.
The site that aghadowey referenced is a good one for sorting through townlands/parishes and counties. (
http://www.thecore.com/seanruad/ ). It allows you to enter just a county name and see all of the townlands with the county. You can then use your browsers search capability (Ctrl F) to help resolve name or spelling issues of specific locations within the county. For example, listing al of the townlands in Co Armagh, and then searching for "James" shows you that there are no townlands, parish's or baronies with james in the name, so ballyjamestown or duff or james-anything, is likely not to be in Armagh.
What do you know about the one born in Monaghan?
Have you tried this site (
http://ifhf.brsgenealogy.com/map.php?&set=yes ) to look for records? You can access the index free of charge. It's a good way to discover information and get some ideas. Unfortuantely Monaghan is not yet online, but the surrounding counties (Cavan, Armagh, Fermanagh) are.
If you can hone in on an area, you might then try ordering 1901 or 1911 Census films from a local Family History Center.
Or you can go back in time by checking the Griffith's Valuation here -->
http://www.failteromhat.com/griffiths.phpEnjoy.
John