If you are using a primary source that's associated with a particular archival repository--either because they own the only copy, or because you accessed it through their website--you may find that they have a preferred citation format for you to use when citing material from their repository. This is to ensure accuracy and standardization in the name and location of the repository and may be vitally important should other researchers attempt to locate your sources.

Before you start to construct your citation for a primary source, check to see if the repository that owns it has listed a preferred citation that tells you how they want you to cite. Many repositories provide this information because it can be challenging to construct a citation on your own, and it also ensures accuracy and standardization in the name and location of the repository, and may be vitally important for other researchers attempting to locate your sources.

You can find an example of a preferred citation statement on the Norwich University Archives website by going to the Services tab and selecting Citing Archival Materials.

You will notice that repositories' preferred citation formats may differ from the format recommended by your assigned citation style (MLA, APA, Chicago/Turabian, etc.). Most repositories would request that you stick to their preferred citation, in order to ensure that the precise information necessary to relocate the collection included. Remember that formal citation styles are intended to encourage overall consistency in format for ease of reading, as well as consistency in the information provided. Primary sources are by nature inconsistent, so a little improvisation is expected. 

If your professor has made it clear that only strict adherence to the assigned citation style will be accepted, just try to include as much of the information from the repository's preferred citation as possible.