There are probably hundreds of great places to ride a bike in northern Illinois but here are three suggestions close to Geneva that will give you a chance to see some of the great fall colors. They may even be areas you haven't visited yet:
The Virgil Gilman Trail from Aurora to Waubonsee Community College is one of the gems of the Kane County Trail system. It is less crowded than the river trail and the section through Bliss Woods is especially beautiful. (About 10 miles from downtown Aurora to Waubosee.)
One of my favorite short rides is to head out to Peck Farm Park and take the loop around the perimeter. It is an easy ride from anywhere in Geneva and provides a nice view of the wetlands. (Peck Farm Park is about 4 miles from downtown Geneva. The loop around the perimeter of the park is about 2.5 miles.)
A ride with a variety of scenery starts from the Persinger Recreation Center at Peck Farm Park. Head west on the trail along the north side of Kaneville Road. Cross Fabyan Parkway at the light at Mill Creek Drive and head south a short distance toward Fabyan Elementary School. Turn west at Grengs Lane and pick up the trail at the entrance to the school parking lot.
Follow the trail all the way around Mill Creek South, staying to the right at the forks in the trail, and continue on the paved path as it curves east past Marklund and across Wyatt Drive. Head south past the playground and turn east to the intersection of South Mill Creek Drive and Main Street. There is a crosswalk that takes you into Dick Young Forest Preserve.
Continue south on the paved path. This trail is part of the Mid-County trail system. This paved stub currently ends near the south end of the forest preserve but there are unpaved trails leading east and west. Heading east will take you around the south side of Nelson Lake Marsh. (About 4 miles from the Persinger Center to the end of the pavement in Dick Young Forest Preserve.)
While enjoying the scenery don't forget to keep an eye out for slippery wet leaves, acorns and walnuts. Darting chipmunks and squirrels add to the thrill of autumn bike rides.