following on from the location clue Matthew posted, there are several baptisms in Mallow around the right time showing on the index on RootsIreland transcripts, including one in the CofI parish in 1817 of one with father first name John, mother's name may be Margaret. You have to pay for credits to see the rest of the details.
For a CofI baptism I wouldn't normally expect a mother's maiden name, and for this date I dont think you'll see father's occupation, but there's a small chance the record might have a slightly more detailed residence than just 'Mallow', i.e. a townland name. You may be able to locate siblings for Thomas based on parents names and parish, assuming they stayed in the same area. Make sure to select the North Cork county centre and Mallow CofI parish, or a search will show dozens if not hundreds of [O']Connells.