Place popcorn in a large, buttered bowl, set aside.
In a saucepan, combine the sugar, butter and corn syrup. Bring to a boil over medium heat; boil and stir until mixture is golden, about 2 minutes. Remove from heat; stir in baking soda and vanilla. Pour over popcorn and toss to coat.
Spread onto buttered cookie sheets and sprinkle with cinnamon and sugar mixture. Cool slightly; break apart while warm. Makes 3 quarts.