This is not an answer or solution, but it's too long for a comment and it might help in finding an answer to this. Sorry if this was inappropriate to post as an answer.
The Simpsons have been known to hide lots of mathematical references in their show (also see The Simpsons and their Mathematical Secrets by Simon Singh, who incidentally also wrote a book about codebreaking).
If this is indeed some kind of code/reference I'm suspecting this is not the only set of codes in the episode. (I might scan the entire episode for more stuff like this later this week).
My first guess is that these are indeed references to US states, which means that some of the answers could be guessed / deduced, leaving us with a partial set of codes and answers. From there the actual method of decryption could possible be deduced, enabling us to solve the rest of the states. However, if these are all just states that wouldn't leave us with much of a puzzle. Hence my reasoning that there is more to this (if at all).
If the codes are indeed states this is not a simple substitution method, where the length of the encrypted text would be the same length as the answer. If it were a substitution code the answers would be truncated to the 6 characters we see, making it a lot harder to solve than with the original lengths. It's possible, but not very likely.
One method of encryption this reminds me of is MD5 (which renders any length of text as a 32 digit hexadecimal number). However, these strings are only 6 characters and seem to use all letters (as well as numbers 0-9) so it's not hexadecimal. It could technically be anything from base 36 up, but as I think it's not a substitution cipher I don't think it's a direct translation from text to any base x format. Then again, MD5 isn't either, so there's probably other known methods of encryption that render fixed-length sets of specific characters. I don't know of any off the top of my head.
Honestly, I think the first step towards a solution is see if we can find a set of answers that might fit the descriptions, like the US states, and see if there's a correlation between the answers and their respective codes.