The best way to find them is to do a google search for maps for your location. There also fire maps like Sanborns that some state libraries make available online to residents. Also try your state historical society as many are now making there collections available electronically.
Check you local County Seat or City hall.
I just pick up some pages from a 1895 Plat book, they were $2.00 per page.
Some of the info on these maps is a Real Help.
We also found a place on the net you can down load them, but it is Real spendy.
Kevin
Our local library has old plat books, the oldest is around 1890. The books can't be checked out, but you can make copies on their copy machine for .10 a page. Shows all the old houses, churches and schools.