Susan,
There are surely many, many options. Keeping them together makes sense, but is there a key central person, such as a matriarch or patriarch, with whom the family is associated? Is there a single most significant event?  Knowing that would help an archivist narrow down their suggestions. 

I'd recommend reaching out to a local archivist to get started. You could also contact the SAA:
https://www2.archivists.org/contact

Sincerely,
Tim

Sent from my iPhone

> On Jun 22, 2017, at 12:55 PM, Susan Walter <[log in to unmask]> wrote:
> 
> June 22, 2017
> Hi All,
> Can someone help me with a documents issue?
> I have several boxes of (mostly) old letters, dating from the 1840s through WWII, that I’d like to find a home for.
> Vermont, Indiana, Illinois, Washington DC, New York, Montana, Panama, New Mexico, Florida, California are some the states these people lived in.
> Subjects range from linguistics, military (Army & Navy), teaching (biology), women’s suffrage, arts (particularly music), social activities, and more.
> Ideally, I’d like to send it as a collection; it is several generations of an extended family.
> S. Walter