Heaven is a wonderful place. God created heaven. It has been stated that only four angels have seen God.
Known inhabitants
God (Ruler)
Jesus (God's son)
Gabriel (This angel has yet to make an appearance in this show)
Lucifer (A fallen angel)
Zachariah (A double agent)
Anna Milton (A fallen angel)
Uriel (A double agent)
Castiel
Unnamed or unidentified angels
Archangels