There was no formal Federal census for Missouri in 1820 because Missouri didn't become a state until 1821 but there are lists of heads of households that are taken from certain areas. The St. Louis Library has an 1820 book but i don't think it lists the heads of households names, rather numbers. But you can get into the website for the library and do a search to see what the book has. You can't search the book itself but it should tell you what's available. It's a great website and if you plan to visit the library it's helpful to look at their searchable lists to see what they have so you can be prepared to spend your time there. Becky