Technically,Bitcoin are stored anywhere.
I think that a better word would be
everywhere.
Your bitcoins are stored in every full node out there: In USA, China, Russia, Brazil, etc.
As every full node has a copy of the entire blockchain, your coins are literally everywhere.
This is a very interesting and innovative concept of money, which we are all still getting used to.
The only thing that is just inside your software are your bitcoin private keys.