Checked baggage on a Domestic → Domestic (connection) → International transit?

Question

I am flying from Orange County, California to San Francisco, California and then on to Seoul, South Korea. If I check a bag will I have to pick it up in San Francisco and re-check it and go through security or customs for the international flight?

Everything I am reading leads me to believe that it's only necessary to re-check baggage and go through security and/or customs when you are first arriving into a country. However, since my first leg is staying within the United States I assume the airline will transfer my bag to the next flight and I can just go straight to the gate for my international flight?

Both legs of the flight are through the same airline (United Airlines) and there are only the two legs: OC -> SF, then SF -> Seoul.

Answer 1

Your bag will be checked all the way through, and you will not need to collect it at SFO.

If you are following the same path on the return journey, then when you check-in in Seoul they will "tag" your bag all the way to SNA (Orange County), however you WILL need to collect your bag in SFO, carry it through customs, and then give it back to the airline. Giving it back to them is a simple step given that it's already tagged - in SFO you simply turn left after you go through customs and you'll come to an area where they will scan the barcode on the tag, put it on a luggage belt, and you won't see it again until SNA!