One book that came to mind reading your list was By the Great Horn Spoon. It’s about a boy who goes to California during the Gold Rush with his butler because his family lost a lot of money in the Great Depression. Even if it isn’t quite what you’re looking for, it’s a lot of fun and it isn’t very long.
The Flavia DeLuce series is small town mysteries, though they are set in England, not the US.
Can’t think of anything else right now, but if I do, I’ll let you know!
Do not be anxious about tomorrow; tomorrow will be anxious about itself.