It states on the 1851 census he was born do to the above residents so Ireland.
I do not know if you have this 1841, census Kilmarnock, its almost certainly the same Mary Henderson.
Address Colledge Wynd,
Henderson Mary, F. age 35 years, born Ireland,
McCree John, M. age 12 years, born Ireland,
Bell Shusan, F. age 11 years, born Ireland,
Lathen Elizabeth, F. age 25 years, born Ireland,
Lathen Robt, M. age 6 years, born Ireland,
Lathen Susan, F. age 2 years, born Ireland,
Ramsay Mary, F. age 20 years, born Ireland.
Same Susan Bell, living with Mary Henderson, correct age for her going by both census.
McCree John, aged 12 years could be transcription error.
No employment data on the census for any of the adults.
Regards,
Jonn.