Re: McKiernan in NJ, just starting my search
Try obtaining a copy of your father's birth certificate, since you already have his date of birth, from the State of New Jersey.This link may help you -
The birth certificate may provide other clues as to more information regarding Margaret McKiernan. Then post any new information you have - her age, etc.
I tried searching for your Margaret on Ancestry's 1930 Census online, but did not find her. I also checked the McKernan spelling. No luck there either.