Check with your local library to see if they give access to Sanborn Maps. Some do, some don't. Also check to see whether your library or state historical society have any plat maps online or available at the library.
As always, Susan is correct.
Also noted by mope540, HMW has great maps, but can be limited.
I've purchased 4 local map copies, pre-1900, from HMW that helped locate a site. They are also affordable. Give or take a few cents, $13 will bring maps to your home with in 3 days.
Peace...