Place popcorn in a very large mixing bowl. (Make sure you remove the un-popped kernels first.)

Melt butter in a small saucepan. Add water, sugar, and salt. Bring to a boil over medium heat and cook for 2-3 minutes. Remove from heat and stir in vanilla and cinnamon.

Drizzle about half of the cinnamon mixture over the popcorn. Stir gently to coat. Add remaining cinnamon mixture and stir till all pieces are coated.