Editing Interstate 39 (section)

{{Short description|Interstate Highway in Illinois and Wisconsin}}
{{Redirect|I-39|the Imperial Japanese Navy submarine|Japanese submarine I-39}}
{{Use American English|date=April 2025}}
{{Use mdy dates|date=November 2015}}
{{Infobox road
|country = USA
|type = I
|route = 39
|map = {{maplink-road|from=Interstate 39.map}}
|map_custom = yes
|map_notes = I-39 highlighted in red
|length_mi = 306.14
|length_ref = <ref name="fhwa">{{Cite web |last=Starks |first=Edward |date=January 27, 2022 |title=Table 1: Main Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways |url=https://www.fhwa.dot.gov/planning/national_highway_system/interstate_highway_system/routefinder/table01.cfm |access-date=December 6, 2023 |work=FHWA Route Log and Finder List |publisher=[[Federal Highway Administration]]}}</ref>
|maint = [[Illinois Department of Transportation|IDOT]], [[Illinois State Toll Highway Authority|ISTHA]] and [[Wisconsin Department of Transportation|WisDOT]]
|established = 1986
|direction_a = South
|terminus_a = {{Jct|state=IL|I|55|US|51}} in [[Normal, Illinois|Normal, IL]]
|junction = <!-- Major junctions only; Only 5-8 most major intersections and cities belong here; please read [[WP:USRD/STDS]] for more info -->
*{{Jct|state=IL|I|80}} in [[LaSalle, Illinois|LaSalle, IL]]
*{{Jct|state=IL|I-Toll|88|CKC}} in [[Rochelle, Illinois|Rochelle, IL]]
*{{Jct|state=IL|I-Toll|90}} in [[Cherry Valley, Illinois|Cherry Valley, IL]]
*{{Jct|state=WI|I|43|WI|81}} in [[Beloit, Wisconsin|Beloit, WI]]
*{{Jct|state=WI|I|94|WI|30}} in [[Madison, Wisconsin|Madison, WI]]
*{{Jct|state=WI|I|90|I|94|WI|78}} in [[Portage, Wisconsin|Portage, WI]]
|direction_b = North
|terminus_b = {{Jct|state=WI|US|51|WI|29}} near [[Rothschild, Wisconsin|Rothschild, WI]]
|states = [[Illinois]], [[Wisconsin]]
|counties = '''IL''': [[McLean County, Illinois|McLean]], [[Woodford County, Illinois|Woodford]], [[Marshall County, Illinois|Marshall]], [[LaSalle County, Illinois|LaSalle]], [[Lee County, Illinois|Lee]], [[Ogle County, Illinois|Ogle]], [[Winnebago County, Illinois|Winnebago]]<br />'''WI''': [[Rock County, Wisconsin|Rock]], [[Dane County, Wisconsin|Dane]], [[Columbia County, Wisconsin|Columbia]], [[Marquette County, Wisconsin|Marquette]], [[Waushara County, Wisconsin|Waushara]], [[Portage County, Wisconsin|Portage]], [[Marathon County, Wisconsin|Marathon]]
|system1={{infobox road/browselinks/USA|state=IL}}
|system2={{infobox road/browselinks/USA|state=WI}}
|browse={{il browse|previous_type=IL|previous_route=38|route=IL|next_type=US|next_route=40}}{{wi browse|previous_type=WI|previous_route=38|route=WI|next_type=WI|next_route=39}}
}}

'''Interstate&nbsp;39''' ('''I-39''') is a north–south [[Interstate Highway System|Interstate Highway]] in Illinois and Wisconsin that runs from an interchange at I-55 in [[Normal, Illinois]], to [[Wisconsin Highway 29|State Trunk Highway&nbsp;29]] (WIS&nbsp;29) approximately {{convert|6|mi|km|spell=in}} south of [[Wausau, Wisconsin]].<ref name="Google2">{{google maps|url=http://www.google.com/maps?f=d&hl=en&geocode=189581027214663335,40.543091,-89.002832%3B6774789599481304502,44.888289,-89.639920&saddr=I-39+N+%4040.543091,+-89.002832&daddr=44.888776,-89.63994&mra=dme&mrcr=0&mrsp=1&sz=15&sll=44.892576,-89.638009&sspn=0.013742,0.028839&ie=UTF8&ll=43.34116,-89.165039&spn=7.222549,14.765625&z=6|title=Overview Map of I-39|access-date=February 15, 2008}}</ref><ref>{{Cite web |date=2012-10-11 |title=Illinois Highway Ends - I-39 |url=http://highwayexplorer.com/il_EndsPage.php?id=3039&section=1 |access-date=2025-01-13 |archive-url=https://web.archive.org/web/20121011012812/http://highwayexplorer.com/il_EndsPage.php?id=3039&section=1 |archive-date=October 11, 2012 }}</ref> In total, Interstate 39 is {{convert|306.14|mi|km}} long.<ref name="fhwa">{{Cite web |last=Starks |first=Edward |date=January 27, 2022 |title=Table 1: Main Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways |url=https://www.fhwa.dot.gov/planning/national_highway_system/interstate_highway_system/routefinder/table01.cfm |access-date=December 6, 2023 |work=FHWA Route Log and Finder List |publisher=[[Federal Highway Administration]]}}</ref> In Illinois, the route has a total length of {{convert|140.82|mi|km}};<ref name="t22">{{cite web |author=Illinois Technology Transfer Center |year=2006 |title=T2 GIS Data |url=http://www.dot.state.il.us/gist2/select.html |access-date=November 8, 2007 |publisher=[[Illinois Department of Transportation]]}}</ref> in Wisconsin, I-39 has a length of {{convert|182|mi|km}}.

Among the newest Interstate Highways in Illinois, I-39 was completed in 1992. Designed to replace [[U.S. Route 51]] (US&nbsp;51) with an [[Interstate Highway standards|Interstate-grade freeway]], the highway [[concurrency (road)|runs concurrently]] with [[U.S. Route 20 in Illinois|US&nbsp;20]] in [[Rockford, Illinois|Rockford]] before joining I-90. From Rockford to [[Portage, Wisconsin]], I-39 and I-90 run concurrently. From [[Madison, Wisconsin|Madison]] to Portage, I-94 joins the two; at {{convert|29|mi|km}}, the three-way concurrency is the longest in the country. From Portage northward, US 51 rejoins I-39, and the Interstate uses its mileposts northward.