<Tr> <Th> GNIS ID </Th> <Td> 421688 </Td> </Tr> <P> The Sangamon River is a principal tributary of the Illinois River, approximately 246 miles (396 km) long, in central Illinois in the United States . It drains a mostly rural agricultural area between Peoria and Springfield . The river is associated with the early career of Abraham Lincoln and played an important role in the early white settlement of Illinois, when the area around was known as the "Sangamon River Country". The section of the Sangamon River that flows through Robert Allerton Park near Monticello was named a National Natural Landmark in 1971 . </P> <P> The river rises from several short headstreams in southern McLean County that arise from a glacial moraine southeast of Bloomington - Normal, Illinois . Part of the moraine is publicly owned as the Moraine View State Recreation Area . The river's course forms a large arc through central Illinois, first flowing east into Champaign County, Illinois, south through Mahomet, then west through Monticello and Decatur, then turning northwest to flow along the north side of Springfield . It receives Salt Creek at 40 ° 7 ′ 33.24" N 89 ° 49 ′ 30.36" W ﻿ / ﻿ 40.1259000 ° N 89.8251000 ° W ﻿ / 40.1259000; - 89.8251000, approximately 25 miles (40 km) north - northwest of Springfield; then the river turns west, forming the southern boundary of Mason County with Menard and Cass counties . It joins the Illinois River from the east just north of Beardstown . </P> <P> The Sangamon is impounded in Decatur to form Lake Decatur, constructed in 1920--1922 to provide a water supply for Decatur . This lake, formed by damming the main stem of the river, with no control over upstream land uses, has had major problems with siltation and agricultural pollution . The lake often has excessive nitrate levels from agricultural runoff . Many times the city was forced to warn people not to allow babies to consume water in Decatur because of "blue baby syndrome", Methemoglobinemia . Decatur has now installed nitrate treatment to avoid this problem . </P>

Where does the sangamon river start and end