|Location||presumably Deceased after taking part in a surprise attack on Lucifer in the year of 2014|
|Episode(s)||5.04 The End|
What, are you stoned?
– Future!Castiel to Dean, 5.04 The End
Future!Castiel is a version of Castiel 5 years into the future of 2009. In 2012, Lucifer's minions re-released the Croatoan demon virus - in this post-apocalyptic world, most humans have been reduced to murderous zombies. Castiel is at Camp Chitaqua with Future!Dean, Future!Chuck and other survivors.
Future!Castiel informs Dean, that sometime after the Croatoan virus was released, the Angels left, and so did most of his angelic powers so that Cas is now effectively human. He can however detect that Dean from 2009 is different from Future!Dean. He is embittered at his situation and has immersed himself in "women and decadence". When Dean first encounters him, he is organsing an orgy, and is a bit out of it.
Future!Castiel is now considered a mortal Angelic Being; in other words he is a powerless angel. The fact that he recognises that Dean is from the future indicates he still has some supernatural power.
He is presumably killed during the attack on Lucifer.
Note: there is mixed opinion amongst fans as to whether the future shown here is "real" or merely constructed by Zachariah to persuade Dean to become Michael's Vessel. Commentary on 5.04 The End on the Season 5 DVDs by Ben Edlund and Eric Kripke supports that this is an alternate universe modeal, rather than time travel.