[Clive]

Just a quick scan of Free Republic discloses that West Nile virous has shown up in:

Alabama, Arkansas, District of Columbia, Florida, Illinois, Indiana, Louisiana, Missouri, New York, North Dakota, Texas

And I am sure that this list is not exhaustive.

The North American locus appears to have been New York.

[B4Ranch]

I wonder how many misdiagnosed cases there has been or cases that went unreported.

[Great Dane]

Alabama, Arkansas, District of Columbia, Florida, Illinois, Indiana, Louisiana, Missouri, New York, North Dakota, Texas

You can add Ohio to the list.