Look over the back yard as a starting point. I believe they are usually out back. You wouldn't want your bathroom in your front yard would you? It should be close enough to the house so that it doesn't take you long to get to it (especially in the winter). But it shouldn't be so close as to stink during the summer. It also has to drain away from the house and from your well (drinking water source). So try about 15 - 30 ft from the back of the house. Look for a slight depression approximately 4 ft square. Since you don't have a probe, find a thin long rod or something slender that is strong. Push it into the ground a couple of places where you think the privy is. It really needs to be at least 3 feet, but less might do. If it slides into the ground all the way down, you may be on the privy. If after a bunch of tries, you can't sink it all the way down, then it's probably not the spot you are looking for. A house that old may have a couple of them, sometimes side by side. Look for that sunken pattern. You can also try Sanbourn Maps, that may have the later privy's on them. Locate where you think it is and do some digging. Talk with some of the other guys on this site to see what you would expect to find early on in the dig. Sometimes it is boring for a couple of feet, but then pay dirt. Be careful not to cut yourself and slow way down if you see any glass, as not to break any whole bottles. I'm sure someone else has some good advice. But if you are going to look for them buy or build yourself a good probe. Good luck and tell us how you do.