multiple data subsets combined in to one variable.

Hi, and welcome. A reproducible example, called a reprex would help here. How the 51 states are broken into locations makes a big difference.

If you have four separate files, say, North, East, West, South"you can mutate each of them with the following pattern using dplyr

north <- north %>% mutate(region = "North")

and then rbind the results into your national data frame.