REGION Codes Expand

Pulling the REGION variable, how do I find out what states correspond to the code values?
1 - Northeast (what states)
2 - North central/Midwest (what states)
etc etc

Also, is there a more detailed code book that would have similar extensions for other variables?

The states contained in each region can be found on the description page for REGION. For most variables, detailed code lists can be found on the variable’s codes page on IPUMS. Here is an example for MSANAME.