So, some other options:

• North Branch trail [high-level-map] [map] [trailhead] <25mins>
• Des Plaines River trail, just east of O'Hare.

• Grant Woods Forest Preserve [topo] [satellite] <1hr> — I have spent some time here, it's fairly fun and hilly for Chicago anyway
• Kettle Moraine State Forest [trail-maps] [wikipedia] <2hrs> —
  • Emma Carlin trail [trail map] [sign] [topo] [KMZ]

Portals (midwest):

• MTB single-track
• ListsOfJohn.com Wisconsin Michigan Illinois
• peakbagger.com Wisconsin Michigan
• peakery.com — highest peaks in: Wisconsin Michigan (NOTE: the site lists them by sea-level height, rather than topological prominence :( )

Portals (entire US):

• list of most prominent peaks
• Ultras — map (yes, there are none east of Colorado)