An amazing deliverance in the Bible is the healing of the demoniac of Gadara.

           It says this man was possessed of one legion of bad spirits.
"Legion" is a military term for a force between 2 to 5 thousand men. The man of Gadara was possessed of that many evil spirits within him.

                   Millions of  evil spirits could be in one place because they don't need physical room. So, thousands can be inside one physical being.