I believe it breaks out like this:
I believe prior to the 80's, there were pretty much a set of Blackhawks on every Earth
. No really, they started out as Quality comics characters, which would have made them in theory on Earth X. Except they had adventures after WWII where the Allies had won, so therefore they were on unofficial "Earth Q" (I might be remembering this designation wrong) which had the Quality characters on an Earth where the Allies won.
Then when "Earth X" was introduced with the same Quality characters, I think they were depicted as being on that Earth too (although this could be wrong - it might have just been the Freedom Fighters characters who lived there.
Then in the late 70's we got the "secret" origin of the JLA that showed the Blackhawks living on Earth 1 as well.
There was a Brave and the Bold where Batman teamed up with the Blackhawks during wartime, so in theory this would have either been Earth 2 or the unofficial Earth B (with Earth B being where all the weird Brave and the Bold stories that didn't fit on one of the regular worlds took place).
Also in the 80's, we learned that the Blackhawks did live on Earth 2 but moved to Earth X in All-Star Squadron #50.
They had their own series in the 80's but I'm not sure which Earth that was supposed to be.