I'm not sure if this is the right forum, but I wasn't sure where to turn. I live in Texas, and I know of a movie theater in the downtown of a very small town, north of the Dallas area, that is over 100 years old. Unfortunately, there's not enough business to keep it open daily, year-round. I am worried that eventually development will swallow up the historical downtown, and the beautiful building will be demolished. I was hoping to figure out how I could get it nominated for a historical marker, and perhaps save part of this community's history.
What you are looking for is the National Register of Historic Places. Every state has a State Historic Preservation Office (or SHPO, pronounced "ship-o") which is responsible for all the historical and archaeological sites in the state. Contacting your SHPO would be the best place to start - public interest is one of the key factors in getting a property nominated for the National Register (as a factor determining the "significance" of the property). That link is for the Texas Historical Commission, the Texas SHPO.
It would be a good idea to contact the owner of the property as well and see how they feel about it. To my knowledge, a property owner can block a nomination in which case it will be even more difficult to get the property protected (by going through the National Park Service). There is a list of benefits for property owners of historic properties, so familiarizing yourself with those might help convince the property owner to help you with the process or at least acquiesce to it.
Just as a caution, but National Register nomination usually takes a very long time so don't expect it to be a quick and easy process. That said, depending on who works in your state SHPO they might be really excited to work with a community member.
Good luck with the project.