Your search ended up here so you may be looking for USA State, Counties or ZipCode boundaries. I do have USA State, Counties and ZipCode boundaries in .shp and .kml format. If you are using Google Maps, you may need .kml file because Google Map only works with .kml file.
- USA State Boundaries in .shp and .kml file
- USA Counties Boundaries in .shp and .kml file
- USA Zipcode Boundaries in .shp and .kml file
Please contact me if you are looking for them.
Updated : I have posted article here about where to download shape file and how you could convert it to kml file.