There are any number of sources for period floorplans, from the 1870's onward plan books were published. Sears and Aladdin (and others) sold houses by mail order, in the form of pre-cut kits or lumber packages. They advertised with plan books. Starting in the 1890's magazines were devoted in whole or in part to architectural designs.
Casey

You might browse through this site: http://www.antiquehomestyle.com/plans

I assume you are really interest in your particular floor plan, not common plans of the era.

If so, you probably aren't going to find the original plans for the home unless it was a kit. Before the modern permit/inspection process, people just built homes how they wanted to and didn't have to file detailed plans with the city/county etc.

That means, you are left with detective work and best guesses. If you have neighbors that have been there for years, they might be a good place to start. The other place to go is the basement and attic.

In the basement, if you see supports running down the center of the house, you probably have a structural wall above them. If you see a second chimney, or the remains of one, you probably are standing under the original kitchen. If you have galvanized drain pipes, you can probably tell where the original sinks, toilets, tubs etc were. Notice which direction the joists run. Walls on the first floor that run perpendicular to them are likely structural.

From the attic, notice the direction of the joists below. The walls below are likely structural if they run perpendicular. Also, if they aren't 1 continuous piece of wood, the joint is being supported by something - usually a load baring wall. You can look for any changes like vents or "missing chimneys" that will let you know what was likely below them. If there is no or minimal insulation, you might be able to see down inside walls. Typically, older houses don't have any fire blocking between studs, so you can sometimes see pretty far into the guts of the home.

Good luck. You may never know exactly what the house looked like, but if you snoop around, you should be able to find some clues. If you combine that with some research about what was common at the time, you may be able to piece together a pretty good "guess."

Thanks for the links and especially all that info! Yes, Bill, I'm really curious about some seeingly odd things, like a bedroom closet that juts into the kitchen - 3 feet after the doorway! I talked to one of the neighbors yesterday (thank gods it's finally getting nice enough outside) and it seems like that closet IS original, however maybe the kitchen doorway was moved over! He grew up here and we've been invited to see how their home is. He's also done a lot of work in our house over the years and offered to walk through and discuss our remodeling thoughts and share what he knows about what was done, so we're pretty excited about that.

Unfortunately during that talk I got the impression that the roof would be better off being replaced within the next year for various reasons. Sigh.