Veteran's Acres Park has a bunch of stuff and is not strictly for biking. If you go into the prarie you can find rolling hills, but go into the woods and find some fun singletrack. There is a major bike trail that goes through the park so nonmountain bikers can enjoy. The only problem is there is not that much distance but you can make tons of loops. The ditance above is an estimate.
How to get there:
The park is on the near the corner of rt. 14 and Walkup Road in Crystal Lake. I recommend parking at the Nature center. To get there take 14 east past Walkup and there will be a sign telling you when to turn left off 14.