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 of Sandra Lee