This trail connects the Paul Douglas Forest Preserve and the Crabtree Nature Preserve in suburban Palatine and Hoffman Estates. The trail is paved, in good repair, and the entire trail runs about 13 miles in length. As seen in the map below (click to enlarge), the trail loops the Douglas Preserve and then parallels Algonquin Road (Illinois Route 62) on a discrete trail alongside the roadway north to the Crabtree Nature Sanctuary.
The trail is the cooperative effort of the Forest Preserve District of Cook County, the Palatine Park District, and the Village of Hoffman Estates.
There are 2 parking lots available. The western-most is off Palatine Road, just a quarter mile or so east of its start at Algonquin Road, at Stover Road. Across the road from the lot is the Crabtree Nature Center entrance and parking lot. You are welcome to use the washroom facilities there, but no biking is allowed on Crabtree's trails since it is a nature sanctuary (but it is a good place to hike!)
The other parking area is off Central Road (alongside I-90 - the Northwest Tollway) at the Grassy Ridge picnic area, east of Barrington Road and west of Roselle and Ela Roads.
The red loop below is measured at 7.2 miles, and the spur trail to Old Stover Road lot is listed as 2.7 miles, so a round trip is about 13 miles in length. For 7 more miles, ride the loop again (I suggest the opposite direction since everything looks different then!)
I began at Grassy Ridge and pedaled west. You traverse lovely woods and meadows and then the trail turns north and parallels Huntington/Freeman Road up to Algonquin Road. You don't realize it visually, but this trail is sneaky-hilly -- no obvious long uphills to pedal, but you are constantly going up and down and getting a fair workout.
There you cross Freeman with a traffic signal and run alongside Algonquin Road as seen here...
As you reach the famous mega-church Willow Creek at Windemere, you cross Algonquin at a traffic signal and then continue west, cross the heavily-traveled Barrington Road at another light, and reenter forest preserve land which you continue on to the Stover Road parking lot and the trail's end.
Return the same way, but upon reaching the Douglas Preserve again at Freeman Road, at the trail intersection, take the paved trail on the left (east) through more lovely woods. When you reach yet another traffic light at Ela Road, cross both roads and pedal the paved trail on the north side of Algonquin Road. At the next intersection, Roselle Road, cross again at the light, and the path continues south alongside the forest preserve golf course.
One last road crossing at Ela, and you're back in Douglas Preserve and on the way back to the Grassy Ridge lot. Since the trail loops the preserve, it's mostly along or near roadways. When it dips into the forest, it's so much lovelier, but even then the overpowering sound of traffic on the nearby roads is a constant reminder that you are in an urban setting.