[mhking]

I'm going to check out Indiana and Ohio, next.

I don't know of any significant tunnels in Indiana outside the handful of caves near the Ohio River; likewise in Ohio.

You might want to check infiltration.org for other data.

http://www.infiltration.org/resources-ohio.html
http://www.infiltration.org/resources-indiana.html

[Hegemony Cricket]

I don't know of any significant wide-area tunnels in Indiana, either; however, downtown Indianapolis has a pretty good network of tunnels for service, etc.