My cousin living in Massachusets inherited abroad a condo 100 K value. If sold there, would it be taxed somehow by Federal or State Gov?

If it belongs to your cousin (who is a U.S. citizen) and he sells it for a capital gain, he must pay taxes on that gain.

WHERE the property is located is irrelevant.

My cousin living in Massachusets inherited abroad a condo 100 K value. If sold there, would it be taxed somehow by Federal or State Gov?
But what is the capital gain in this case? All 100K to be taxed? Condo is old, I don't think he has any clue on its purchase price...

No, the capital gains tax will be assessed on the difference between the sale price and the stepped-up value at the time of the death of the orinal owner, which is based on Fair Market Value on the day of the death.

Bottom Line: He probably will NOT owe that much in tax.