Hell

The Hell is the place or punishment and pain of the afterlife. Human souls who are sent to Hell are tormented until their humanity is stripped away and they become demons.

Dean spends four months in Earth time in hell, but he reports that time passes differently there, and for him it was more like forty years. This makes 3 days on earth roughly equivelant to a year in Hell. Satan is the ruler of hell. Satan has millions of Demons under his command. Hell was created by God, Lucifer and the fallen were thrown into hell by the archangel Michael.

Inhabitants who were in Hell for a brief period of time
Dean Winchester 

Castiel

Lilith

Known inhabitants
Lucifer/Satan (King)

Azazel (Lucifer's son)

Cerberus (Leader of the Hellhounds)

Hellhounds (executors)

The Demons of Hell (Lucifer's servants)

Alaistair (chief torturer)

Lilith (queen of demons)

Current leaders
The Demons of Hell (Possibly; in Lucifer's absence)