Steps about half way down about how to remove the files.
If no mods then go here:
C:\"Your Install Location"\Steam\userdata\"Your User Number"\241540\local
Delete all files in this folder (Your Saves), can also be done in the profile manager in-game. Also delete StateOfDecay.exe & then verify the game integrity through Steam.
If all else fails kill the install and redownload, you are not alone numerous people have reported issues with this patch however starting from scratch has fixed most of them.