Hello again Áine!
I assume Robert was RC. (If I'm incorrect, let me know).
As you likely know, the RC records for that area (Ballymore) start in 1824. I also checked the Tithe records and although there were over 60 Carey records in Westmeath, none were in Killare parish.
The Griffiths Valuation showed one Carey in the parish http://www.failteromhat.com/griffiths/westmeath/killare.htm