How to locate a tournament? Basically there are 6 ways.
First search on uschess.org, with this link: https://new.uschess.org/upcoming-tournaments. You can search for your state or nearby states. Many states have their tournaments listed there, but not everyone does.
So second, check your state organization website. It may be called federation, such as NJ, or association, such as Ohio. Doesn't matter which name. Just search for "state name chess association" you should be able to find the website. Usually there is a page listed with recent tournaments.
Third, if you know which school or which organization is organizing tournaments, go to their websites. They should have a schedule for future tournaments.
Fourth, some states may have some aggregation sites for scholastic tournaments, such as New York City. It has http://luckfactory.com/nyc_chess_calendar.html.
Fifth, use CCA website: https://chessaction.com/ They always organize big tournaments. Their tournaments are also listed on uschess.org.
Last, ask other parents. Also you go to tournaments or classes, watch out for handouts.