Dropping the cigarettes onto the crowd, in the last midnight town square gathering, was actually done by putting 8" diameter, 25'-long pipes against the trees in the town square. The pipes were then filled with cigarettes. Then, on cue, air was blasted into the pipe bottom, shooting them into the air and onto the crowd. After each take everyone was asked to gather up the cigarettes from the ground and turn them in so they could be reloaded into the cigarette canons and rained down again. The filming of this final scene took several weeks in the late fall in Iowa where it is pretty cold. In the movie it is supposed to be summer time so the actresses are dressed in summer dresses. Between takes, everyone (actors and extras) were huddled in winter coats sucking on ice cubes. The ice cubes kept their mouths and breath cold so there would be no visible vapor when they exhaled.
During the off days of filming, in Iowa, Dick Van Dyke rented a car to drive around the open spaces and small towns locally. He ran out of gas one day, and sat on the roof of his car whistling by putting a blade of grass up to his teeth and blowing. A farmer happened by and gave Van Dyke a lift to get gas.
The bulk of the film was shot in Greenfield, Iowa, with many of the actual residents playing extras in many scenes.