Preheat the oven to 250 degrees. Place the popped popcorn into a large mixing bowl and set aside.
Melt the butter and sugar in a small saucepan over medium low heat. Remove from the heat & stir in the cinnamon and vanilla. Pour over the popcorn, and mix until the popcorn is evenly coated. Spread the popcorn into a large greased roasting pan.
Bake in the preheated oven 10 minutes, stirring after 5 minutes. Remove from the oven and cool before serving.