The Plum River is a tributary of the Mississippi River, about 46.6 miles (75.0 km) long,^[1] in northwestern Illinois in the United States.^[2] It rises in Jo Daviess County and flows generally south-southwestwardly into Carroll County, where it joins the Mississippi at Savanna. Among its several short tributaries are:

• The East Plum River, which rises in Stephenson County and flows southwestwardly into Carroll County, joining the Plum at 42°10′16″N 90°01′20″W / 42.1711111°N 90.0222222°W / 42.1711111; -90.0222222 (East Plum River mouth)^[3]
• The Muddy Plum River, which flows for its entire length in Jo Daviess County. It joins the Plum River at 42°13′35″N 90°01′45″W / 42.2263889°N 90.0291667°W / 42.2263889; -90.0291667 (Muddy Plum River mouth)^[4]
• The Middle Fork Plum River joins the Plum River at 42°16′29″N 90°02′12″W / 42.2747222°N 90.0366667°W / 42.2747222; -90.0366667 (Middle Fork Plum River mouth)^[5]
• The North Fork Plum River has its confluence with the Plum River at 42°15′46″N 90°02′33″W / 42.2627778°N 90.0425°W / 42.2627778; -90.0425 (North Fork Plum River mouth)^[6]