Is Illinois a Tenancy by Entirety state?

Yes. The tenancy by the entirety was created in Illinois in 1990. See this article for more information: http://cmetro.ctic.com/TitleIssues/v1n7.pdf

The tenancy by the entirety statute is found at Section 1c under the Illinois Joint Tenancy Act found at 765 ILCS 1005/1.