Illinois Route 100

Illinois Route 100
State	IL
Type	IL
Route	100
Length mi	159.09
Established	1924
Direction a	South
Terminus a	Alton
Direction b	North
Terminus b	Webster
Counties	Madison County, Jersey County, Calhoun County, Greene County, Pike County, Adams County, Brown County, Sangamon County

Illinois Route 100 is a north–south state highway in the U.S. state of Illinois running along the east and west banks of the Mississippi River for much of its length between Alton and Webster. The route connects river towns, historic sites, and transportation nodes, intersecting major highways and serving as a corridor for tourism, freight access, and local traffic. IL 100 passes through landscapes associated with river commerce, conservation areas, and communities with links to regional history such as the Lewis and Clark Expedition, Lincoln-Douglas debates, and riverboat heritage.

Route description

From its southern terminus near Alton, IL 100 follows riverfront alignments adjacent to the Mississippi River and parallels infrastructure like the Old Chain of Rocks Bridge, Clark Bridge, and rail corridors of the Missouri Pacific Railroad and Union Pacific Railroad. The highway serves river towns including Grafton, Hardin, Kampsville, and Pittsfield, and provides access to sites such as the Pere Marquette State Park, Jersey County Courthouse, and the Fort de Chartres State Historic Site. IL 100 intersects federal and state routes including U.S. Route 67, Interstate 255, Illinois Route 3, Illinois Route 96, and Illinois Route 106, acting as a connector to the Great River Road and local ferry services like the Kampsville Ferry and Golden Eagle Ferry that maintain links to Missouri River and Missouri crossings. The corridor crosses floodplains, bluffs, and agricultural lands near the Illinois River confluence, skirting features tied to the Mississippi Flyway and conservation areas administered by the Illinois Department of Natural Resources and organizations such as the Sierra Club and Audubon Society.

History

Designation of the corridor began in the 1920s during statewide numbering efforts influenced by policies in United States Numbered Highway System planning and civil engineering practices emerging from work by figures like John McAdam-era roadmakers and later highway advocates akin to Bureau of Public Roads. Early realignments occurred in response to river flooding episodes documented alongside events such as the Great Flood of 1927 and local levee projects overseen by the Mississippi River Commission and the United States Army Corps of Engineers. During the mid-20th century, improvements paralleled regional investments tied to New Deal infrastructure funding and later interstate-era shifts associated with the construction of Interstate 70 and Interstate 55, which altered through-traffic patterns. Preservation efforts in the late 20th and early 21st centuries involved collaboration with agencies including the Illinois Department of Transportation, heritage groups connected to National Park Service-administered programs, and local historical societies preserving sites like Fort Grafton and riverfront districts influenced by steamboat commerce and figures such as Samuel Clemens (Mark Twain) and explorers like Meriwether Lewis and William Clark.

Major intersections

IL 100 intersects and overlaps with several numbered routes and transportation nodes, including: junctions with U.S. Route 67 near Godfrey, interchange access to Interstate 255 that connects to the Gateway Arch region of St. Louis, concurrency segments with Illinois Route 3 along the western river corridor, crossings near Illinois Route 106 toward Carlinville, and links to Illinois Route 96 near Pittsfield. It provides proximity to rail hubs serving Amtrak corridors and regional freight services by BNSF Railway and Canadian National Railway, and connects to local ferry terminals such as the Kampsville Ferry and the seasonal Golden Eagle Ferry facilitating crossings to towns like Steelville-area routes and access to Missouri State Highway System crossings. The route interfaces with county roads administered by county boards in Madison County, Jersey County, Calhoun County, and others.

Scenic and recreational significance

As part of the Illinois Great River Road, IL 100 offers scenic vistas of the Mississippi River bluffs and migratory corridors used by species commemorated by the Audubon Society and state wildlife programs. The route provides direct access to recreational assets such as Pere Marquette State Park, canoe and kayak put-ins used for river recreation chronicled in guides by organizations like the American Canoe Association, fishing areas managed under the Illinois Department of Natural Resources license system, and heritage tourism tied to Lincoln Home National Historic Site-adjacent circuits and riverboat history celebrated at museums and festivals such as the Great River Road Festival. The highway supports birding trails, access to the Chain of Rocks Canal and recreational trails connected to municipal parks in Alton and Grafton, and proximity to vineyards and agritourism enterprises in the region promoted by the Illinois Tourism Board and county convention and visitors bureaus.

Maintenance and traffic

Maintenance responsibility lies with the Illinois Department of Transportation which coordinates with local county highway departments and the United States Army Corps of Engineers for flood-control-related repairs. Traffic on IL 100 ranges from local commuter flows in the Alton area to seasonal peaks tied to tourism and events in Grafton and state parks; commercial freight uses access points to the Interstate Highway System and rail interchanges. Roadway treatments have included resurfacing projects funded through state appropriations and federal aid administered under programs similar to the Surface Transportation Program and coordination with the Federal Highway Administration for safety improvements, signage upgrades consistent with the Manual on Uniform Traffic Control Devices, and bridge inspections aligned with National Bridge Inspection Standards.

Future developments and proposals

Proposals affecting the corridor have included multimodal improvements emphasizing scenic byway designation continuity with the Great River Road National Scenic Byway, ferry modernization projects supported by regional planning commissions like the Metropolitan Planning Organization for the St. Louis metropolitan area, and resilience investments addressing flood risk in partnership with the Federal Emergency Management Agency and the Mississippi River Commission. Potential state-level initiatives discussed by the Illinois General Assembly and IDOT involve enhancement of shoulder widths, safety realignments near high-crash locations, and coordination with economic development agencies and local chambers of commerce to balance tourism, freight, and conservation priorities. Stakeholders such as conservation non-profits including the Nature Conservancy and local historical societies remain active in shaping preservation-oriented proposals for the corridor.

Category:State highways in Illinois Category:Great River Road