Technically the businesses can be older, but they can't be "US businesses" for longer than the US existed. That doesn't take away from the spirit of your point, though.
I'm now very curious which companies have managed to survive major ownership changes in their nation-of-business, and whether there was continuity of management/shareholdership in those cases or not. Hong Kong would probably be pretty easy to study for that.
The Hudson's Bay Company used to be the owner of its nation-of-business (Rupert's Land, now western Canada). Today it's a department store chain in Canada and the parent company of two chains (Lord & Taylor and Saks Fifth Avenue) in the US.
The handover caused very little, if any, disruption to business in Hong Kong. The city still runs itself for all intents and purposes as an independent country, just with a new flag on the mast.
The most recent handover was minimal, yes. I'm more curious as to whether any single organization in Hong Kong existed prior to 1842 that still exists today, thus having survived two sovereignty changes.
Macau would probably be a better subject if that's your aim. There was almost nothing in Hong Kong before the opium wars -- a couple of thousand people in fishing villages -- but the Portuguese were in Macau for ~400 years. Unfortunately, I'm not very well versed on the latter.
I imagine that it would be even easier to look at European companies, as there has been lots of border changes there.
According to a quick search into Finnish companies, the currently oldest one (Fiskars, founded in 1649) has survived the transitions from Swedish rule to Russian rule (1809) and to independence (1917). The owners have changed several times. The oldest one that remained in the same family seems to be Frenckells printshop, which survived from 1642 to 2008.