There’s only ever been one state secede from their parent state to make a new state: West Virginia.
Scratch that. It has happened 4 times: a new state is formed by leaving the parent state. The most recent one was during the US Civil War and was West Virginia. Yes, it is allowed by the Constitution (Article 4 allows it)
Might we see it in my lifetime? There’s a movement afoot for part of Colorado to secede and make a new state (or join with Wyoming). Now, I’d prefer the new state route….the Senate has been stuck at 100 for quite some time. It would also give an opportunity for some new conservative blood in the Senate.
[Update 2013-10-07 16:23:46] I can’t count. It should have been 4 instead of three. I’ve update the article
image from jessie 1974 via flickr