Prepare popcorn in microwave according to package directions. Pour popcorn into 1 or 2 large bowls. (You will need plenty of room to toss with hot sugar mixture.)
Meanwhile, in a small saucepan over medium heat, melt butter. Add water, sugar and cinnamon, increase the heat, and bring to a boil. Boil for 3 to 4 minutes. Remove from heat. Be careful; the sugar mixture is extremely hot! Pour half of mixture over the popcorn. Carefully stir or toss to combine. Add remaining sugar mixture and combine. Serve.
Recipe courtesy Sandra Lee