It enters Illinois in Jo Daviess County to flow through the city of Galena before it joins the upper Mississippi River a few miles south and west.

This region was ice-free during the Wisconsin glaciation and underwent hundreds of thousands of years of glacial-free erosion.

The indigenous gave it this name because in the early days of this country, some of the warriors existing on the present site of Galena and the banks of a small creek a little south of town, went to the assistance of their eastern brothers.

As early as 1822, the "City" of Galena was mentioned in newspapers while Chicago was referred to simply as "a village in Pike County containing 12 or 15 houses and about 60 or 70 inhabitants".

Galena was more important commercially than Chicago at this time; it served as a trading point and provided work at its nearby lead mines.