Are there any places in the us or elsewhere where organ donation is an opt-out?

Yes: If you are not interested in being an organ donor while you are alive or after you have passed, make your feelings known to your family and next of kin. In the United States your organs will not be removed without your permission if you are alive, or without permission from your next of kin if you have died.

No: Everywhere that i know of, organ donation is an opt-in. In other words, the default position if you never make your wishes known is that your organs are left in your body. If you want them donated, you have to make your wishes known in order to donate them.