The Little Vermilion River is a tributary of the Illinois River, which it joins near LaSalle, Illinois, opposite the north-flowing Vermilion River. There is another "Little Vermilion River" in Illinois which is a tributary of the Wabash River.
Approximately 75% of the land () of the land in the watershed is devoted to agricultural activities, primarily corn () and soybean () production. Native wetlands account for 0.5% () of land in the watershed.
An EPA report lists the southern section near La Salle, Illinois as impaired waterway due to excessive zinc from current and historic mining operations. It is also listed for elevated fecal coliform bacteria levels due to the use of combined sewage overflow systems in use by several municipalities within the watershed.