Collectors often look for paper money in a couple of ways for their collections. They will look for a certain bank, city, or even state that the money was produced in.
If there was a major metropolitan area, the more banks were likely to be there. The east coast area has quite a few different banks that offered paper money. This was true to just past the Mississippi river. The farther west you went, the fewer banks you would run into. The gold rush in California that started in 1848 was what helped bring some banks (and eventually a United States mint in San Francisco) that far west.
Even up north in places like North Dakota, Washington State, and even Alaska have very few banks at all. There have been a few bills (collectors also call them “notes”) to turn up for a few banks in these states, and are highly sought after.
What fun direction can your collection go?