"In theory" any state could have seceeded. If you want to posit a complete collapse of Federal authority for some reason in 1860 fine, and this could even be interesting. But if you want to posit the midwestern non-slave states joining the Southern Confederacy in the OTL American Civil War this is completely implausble. And if you want to see a map, just print a blank one out from the internet and color which ever states you want in CSA gray.