Hey @Matt Sheridan, thanks for taking the time to post to the Dropbox Community.
If you have the Dropbox desktop app installed on your computer, you should already have a local copy of your Dropbox files on your hard drive.
With the desktop app, Dropbox creates a local Dropbox folder and syncs all your files to it, so any changes you make to your files online, will sync locally and vice versa.
This won't be a backup folder, but you can use it to create copies of your files in other locations for safekeeping, if you want.
I hope this helps, but let me know if you have any questions.