marriage

[comfort]

hi
if some one was living  on govenor road in londonderry in about 1920,and they were catholics were would they most likley get married,
also
i have a birth certificate  for 1923 saying
the birth registed in the district of londonderry
no 2 in the union of londonderry in the county of londonderry
what dose no2 in the union mean
any help would be welcome
thank you
patricia