[1] Illinois Route 25 was opened in August 1929; it originally ran from Elgin to East Dundee.

The entirety of this road follows part of the Fox River on its eastern bank.

It then winds through North Aurora and Batavia, lacking an interchange with Interstate 88.

After this, the road passes through Carpentersville, and finally ends at Illinois Route 62 in Algonquin.

Mileposts are given in distances from southern terminus, while mileage under county names reflects IDOT surveying.