One of the great things about React is the advice that you can put more in a single file than you used to be able to. We seem to have forgotten that concept when it comes to the data layer of most Redux applications I see.
I would suggest that people check out the Ducks pattern: https://github.com/erikras/ducks-modular-redux
To sum it up: your constants, action creators, action handlers, and reducer all go in a single file. You can export anything you need from a duck file, and the default export for any duck must be the reducer. This ends up being really nice - no more rapidly switching back and forth between action creator files, reducer files, your constant files, etc. It also allows you to easily collect all your ducks and attach them to a redux store (thanks to the default export.)
Some suggest putting any data fetching in the ducks as well - I think this can be handled on a case-by-case basis - I tend to prefer to keep my data managers in a separate "services" folder though, which are just files that export async functions like "fetchUser(id)" or "fetchArticles()"
Ultimately there are many different valid ways to structure your code, this is just one way that I've found to be much more enjoyable.