Away from the national or state-level collections, archival collections may be found all over America in various research libraries - private institutions, public libraries or university libraries. What they hold and how easily they may be accessible varies as much as the institutions do themselves. It can be daunting to know how to start identifying useful collections or work out what you need to do to visit and gain access. In general, the tips on the first page of this guide apply: do your research on their collections as best you can before you go, and always contact them in advance to make arrangements for your visit.
Listed below are some particularly significant institutions, but the best way to identify archival collections of interest is to use the various catalogues and finding aids. Once you know where a collection is held, you will be able to look for further details, finding aids or digitised materials from that institution, and begin to make arrangements for any visit. Be aware that university libraries in particular may have restrictions on when you can visit, and you will probably need to show proof of your own university status (so always take your university card with you as well as your passport).
The following links and guides are useful tools for locating archival collections in various institutions in the United States. See the separate US History Sources guide for information on locating archival collections relating to the United States in the UK.