The Bible never gives an exact headcount for a “legion.” The word is borrowed from the Roman army, where a legion at full strength numbered about 5,000 soldiers. Hop over here to read about the “twelve legions of angels,” or see this informative post on the Roman legion.
Where the Bible Uses the Word
“Legion” appears three times in Scripture, and every time it means an overwhelming number, not a fixed count. A demon-possessed man used it to describe the many spirits in him:
“What is your name?” Jesus asked. “My name is Legion,” he replied, “for we are many.” (Mark 5:9)
Jesus used the same word for angels, telling His captors He could call on far more help than any army could field:
Are you not aware that I can call on My Father, and He will at once put at My disposal more than twelve legions of angels? (Matthew 26:53)