The Leaf River is a tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Rock River, about 31 miles (49.9 km) long, in northwestern Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. Via the Rock, it is part of the Mississippi River

Mississippi River

The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

.

Course

After rising east of the town of Shannon

Shannon, Illinois

Shannon is a village in Carroll County, Illinois, United States. The population was 757 at the 2010 census, down from 854 at the 2000 census. Shannon is home to three churches, Shannon Baptist, St...

 in northeastern Carroll County, the Leaf flows eastward across northwestern Ogle County

Ogle County, Illinois

Ogle County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 53,497, which is an increase of 4.8% from 51,032 in 2000. Its county seat is Oregon, and its largest city is Rochelle...

, past the towns of Adeline

Adeline, Illinois

Adeline is a village in Maryland Township, Ogle County, Illinois, along the Leaf River. The population was 85 at the 2010 census, down from 139 at the 2000 census.-Geography:Adeline is located at...

 and Leaf River

Leaf River, Illinois

Leaf River is a village in Leaf River Township, Ogle County, Illinois, along a stream of the same name. The population was 443 at the 2010 census, down from 555 at the 2000 census.-Geography:Leaf River is located at ....

. It joins the Rock River from the west between the towns of Byron

Byron, Illinois

Byron is a city in Ogle County, Illinois, United States, probably best known as the location of the Byron Nuclear Generating Station, one of the last nuclear power plants commissioned in the United States. Byron is located in Byron Township, along the Rock River. The population was 3,753 at the...

 and Oregon

Oregon, Illinois

Oregon is a city located in Ogle County, Illinois. As of the 2010 census, the city had a total population of 3,721, down from 4,060 at the 2000 census. It is the county seat of Ogle County.- History :...

.