The Supreme Court (and other courts) have held mandatory quarantines to be legal, including of entire areas and not just persons known to be infected.

It would logically follow that if the quarantine is legal, penalties for violating it are also legal.

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Most of those cases are quite old, but they're still the ruling precedent on the topic as far as my (limited) knowledge goes.

For one that went to the Supreme Court in 1902 and continues to be cited:

Compagnie Francaise de Navigation a Vapeur v. Louisiana Board of Health

https://en.wikipedia.org/wiki/Compagnie_Francaise_de_Navigat...

If enforcement action happens now, we'll still have a functional Supreme Court around in a year in order to debate it.

Maybe, let's see how it works out. I have no skin in this game. Numbers will talk in the next weeks and months, in the meantime all I can say is that I'm glad I'm not in the US right now.

Doubt it, and in any case, that would be years down the line. It wouldn't help you one whit if you've got police ordering you back into your house now.

Which might be reasonable if there are flagrant violators and things continue to get worse.

States have pretty broad police powers especially in times of crisis. It wouldn't surprise me to see the 10th Amendment apply to the state action of enforcing massive quarantines.

While that's definitely true, this is also inherently running up agains the Bill of Rights. Police powers are not unbounded so as this continues (and especially as it subsides), I expect legitimate unanswered questions of Constitutionality could come into play.