Illinois Route 25 follows the east shore of the Fox River through the Fox Valley in Kane County and northeastern Kendall County. For its entire length, it lies across the river from Illinois Route 31, which follows the west shore of the river. It runs from Algonquin to Oswego, passing through Elgin, St. Charles, Geneva, Batavia, Aurora, and other riverside towns.
The northern end of Illinois 25 is at Illinois 62 on the east side of Algonquin:
Illinois 25 crosses Illinois 68 in East Dundee, near that route's western end:
Now within the city limits of Elgin, Illinois 25 reaches the western extent of Illinois 58:
In the heart of Elgin, Illinois 25 meets the western endpoint of Illinois 19:
Near the point where Illinois 25 crosses under US Route 20, a pair of side streets leads to a makeshift fountain interchange accessing Route 20 which behaves as a freeway. I'm hesitant to give US Route 20 full freeway status, though, because this interchange is comprised of ramps with dangerous sharp curves: