Reilly & O'Reilly and other variations is one of the most common names in Co. Cavan so I do not doubt that there were more Thomas Reillys born in 1835
Killeshandra is one of the few places that still has a census for 1841 and it includes the townland Drumcrow, it may be one of the avenues that would help you sort out your dilemma.
There are a number of Drumcrows, this site give you all the names of the townlands and their locations https://www.townlands.ie/search/?q=Drumcrow
I hope I have not confused you.
Best Wishes Carmel