Finding records on an anscestor's (US) naturalization

I’m trying to figure out when and how my grandfathere became a citizen of the United States. I know he arrived in the United States in the 1920s at the age of 8 with his mother and sister. What I don’t know is when and under what circumstances he became a US citizen.

How would I go about finding information on this?

Is it likely that he became a citizen when his father gained citizenship?

Check out this site which has links to naturalization records in the various states. I think that the best way to find out about your grandfather is to ask your parents (if they’re still around) or relatives who might know. Maybe you can gain access to your grandfather’s papers. Yes, it is possible that your grandfather was a citizenship at birth (outside the U.S.) if his father was already a U.S. citizen. But that would mean that you will need to know the citizenship status of your great-grandfather at the time that your grandfather was born. Good luck in your search.