Illinois River (Colorado)

{{Use American English|date=February 2025}}

{{More citations needed|date=January 2011}}

{{Infobox river

| name = Illinois River{{cite gnis|id= 170358 |name= Illinois River|accessdate= 2011-01-31}}

| image = DSCN2571 illinoisriverinwalden 600.jpg

| image_alt =

| image_caption = Illinois River in April from SH 14 south of Walden

| map =

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| source1_location = Never Summer Mountains

| mouth_location = Confluence with Michigan

| mouth_coordinates = {{coord|40|45|08|N|106|18|11|W|region:US|display=inline,title}}

| progression = Michigan—North Platte—Platte—
Missouri—Mississippi

| length =

| source1_elevation =

| mouth_elevation = {{convert|8022|ft|m|abbr=on}}

| discharge1_avg =

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Illinois River is a tributary of the Michigan River, approximately {{convert|71|mi}} long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. [http://viewer.nationalmap.gov/viewer/ The National Map] {{webarchive|url=https://web.archive.org/web/20120329155652/http://viewer.nationalmap.gov/viewer/ |date=2012-03-29 }}, accessed March 21, 2011 in Jackson County in north central Colorado. It drains part of the North Park basin south of Walden.

The Illinois River starts in the Never Summer Mountains near the continental divide, just south of Farview Mountain. It descends northward through a winding gorge, emerging into North Park at approximately {{convert|8000|ft}} above sea level. It flows northward through the valley as a winding stream, past Rand. It passes under State Highway 14 just southeast of Walden and joins the Michigan from the north just north of Walden. A portion of the valley of the river south of Walden is located within the Arapaho National Wildlife Refuge.