National Cinema Day is a special day where movie tickets are sold at a discounted price of $4 at participating theaters across the United States. According to the search results, more than 3,000 theaters are participating in National Cinema Day this year. Theaters participating in National Cinema Day are not limited to a specific chain or location, and the number of participating theaters may vary from year to year. Therefore, it is recommended to check with local theaters to see if they are participating in National Cinema Day. Some search results provide a list of participating theaters in specific locations, such as Kansas City.