The Illinois Department of Transportation (IDOT) applied for the designation of Interstate 39 to the American Association of State Highway and Transportation Officials (AASHTO) on October 22, 1984:
The freeway in the U.S. Route 51 corridor from Rockford south to Illinois Route 5 is built to Interstate standards. The segment south of Illinois Route 5 to Interstate Route 80, presently under construction, also meets Interstate standards. Therefore, we are proposing that this 64 mile segment of freeway between FAI 90 at Cherry Valley and FAI 80 at LaSalle/Peru, be designated as Interstate Route 39 under Title 23 U.S.C. 139(b). This route would provide a direct connection between Interstate Route 80 and Interstate Route 90 and would serve the Rockford Metropolitan area which as a population of over 200,000.
AASHTO disapproved the application on December 8, 1984, instead recommending a three digit spur. However after reconsideration, the Route Numbering Committee approved a subsequent request by IDOT on January 3, 1985 for the establishment of I-39 in a letter dated February 5, 1985.
When proposed in 1984 as I-39, the freeway along U.S. 51 was only constructed between former IL 5 (East-West Tollway/I-88) and U.S. 20 at Rockford. The section between IL 5 and Interstate 80 opened in 1986.
AASHTO approved an extension of Interstate 39 south from I-80 at LaSalle/Peru to I-55 at Bloomington subject to Federal Highway Administration (FHWA) concurrence on June 10, 1986. This section initially opened to traffic from I-80 south across the Illinois River to IL 251 (old U.S. 51) in December 1987. The remainder of I-39 south between IL 251 and Bloomington-Normal was constructed between 1987 and 1992.
Separate applications by IDOT and the Wisconsin Department of Transportation (WisDOT) for the northward extension of Interstate 39 from Rockford, Illinois to STH 29 in Wausau, Wisconsin were approved by AASHTO on October 22, 1993. The IDOT application added 19 miles from I-90 near Rockford to the Wisconsin state line. The WisDOT application cited the addition of 182 miles for I-39 in the state, with 103 miles independent of another Interstate highway.
The full installation of signs acknowledging I-39 along the overlap with I-90 and I-94 in southern Wisconsin was a slow process. The mainline was well posted with reassurance markers, but intersecting roads generally omitted the I-39 designation until at least 2003. One signing oddity was made in the city of Madison, where instead of signing I-39/90/ 94 with three separate signs, a single blank Interstate shield was used instead. These trailblazers were posted near East Towne Mall, which is located southwest of the interchange joining U.S. 151 with I-39/90/94.1
Construction on Interstate 39 was initiated in the late 1970s and early 1980s. The following chronology shows the construction time line of I-39, including information provided by Steve Sarver and Robb Haukohl:2
- 1984 – Interstate 39 opened from U.S. 20 near Rockford to IL 5 near Rochelle.
- 1986 – Interstate 39 extended from IL 5 to I-80.
- December 1987 – the section from Interstate 80 south across the Illinois River was opened and its southern terminus was IL 251 (old U.S. 51). It was not open from IL 251 to IL 71. Named the Abraham Lincoln Memorial Bridge, the one mile long crossing is the longest span in Illinois.
- Late 1988 – construction began on the interchange with Interstate 55 in Bloomington
- Summer of 1990 – Interstate 55 was reconstructed around Normal with an additional lane of traffic. The existing interchange joining U.S. 51 and I-55 was closed completely and then reconstructed with its present configuration. Bridge work continued for the overpasses between Normal and Oglesby. The section from Oglesby to Normal utilizes a unique style of overpass construction that allowed for the elimination of the center pier. U.S. 51 was rerouted onto the I-55/74 bypass around Bloomington-Normal, and the main route town was designated as U.S. 51 Business (AASHTO action taken established U.S. 51 Business on June 2, 1990).
- Summer/Fall of 1991 – segments of the new highway were opened south to IL 18.
- May 29, 1992 – 4.4 miles of I-39 opened between Hudson and Kappa.
- October 31, 19923 – final segment of Interstate 39 opened, completing the entire freeway from Rockford to Bloomington. IL 251 extends on most of the old U.S. 51; some minor rerouting was necessary because the new four-lane highway was built directly on top of the previous two lane road. IL 251 concludes at I-39, 7.5 miles north of Normal, while the four lane U.S. 51 Business was constructed over old U.S. 51 for 1.75 miles beyond Normal. There is a no section old old U.S. 51 in tact between the two routes.
- Mid-1995 – The Willow Creek Rest Areas opened on both sides of Interstate 39 between Exit 82 and Exit 87. Grading for their ramp system was completed some time before the facilities were built. Also, before the rest areas opened, weigh stations operated along on both sides of the freeway, 17 miles to the north. These were later closed and fenced off to prevent access.
- 1998-1999 – Interstate 39 extended northward into Wisconsin. Signage was placed first on the U.S. 51 freeway from Portage north to Wausau, and eventually along the overlap with I-90/94. The 1999 Rand McNally North American Road Atlas was the first to show Interstate 39 along in the Badger State.
- 2003-2004 – Toll collection at the Cherry Valley Interchange in Rockford, where I-39 separates from I-90, was eliminated for southbound. Tolling along I-39 northbound at the exchange ceased in November 2004.
- April 17, 2003 – E.J. ‘Zeke’ Giorgi Highway designated along Interstate 39 between I-88 (Ronald Reagan East-West Tollway) and the Illinois-Wisconsin State Line. Representative Zeke Giorgi pushed for the construction of I-39 through Northern Illinois.4
An extension of Interstate 39 north from Wausau to Merrill along U.S. 51 remains a possibility. Craig Holl wrote WisDOT to determine whether plans called for upgrading this stretch of U.S. 51 into I-39. Douglas Ross responded in October 2002,
The DOT is currently using design standards that will satisfy requirements for an Interstate Highway, to develop plans for the reconstruction of the segment of USH 51/ STH 29 between Fox Glove Road and Bridge Street. To the best of my knowledge, the Department has no plans at this time to formally request that I-39 be extended; however, if the request is made in the future this segment of roadway should meet the design standard requirements after the reconstruction is completed.
Started in 2004, a major project upgraded the freeway along U.S. 51 around Wausau to Interstate standards.5
Costing $291 million, the US 51/WIS 29 project reconstructed seven miles of U.S. 51 and Wis 29 between Foxglove Road and Bridge Street in Marathon County. The road was rebuilt into a six lane freeway between the east and west interchanges with STH-29, with auxiliary lanes added as well. Work also included a revamp of the east and west U.S. 51 connection with STH-29 into high speed systems interchanges. The east interchange was completed in 2006 and three of the four ramps at the west interchange were open to traffic in 2008. Overall construction was completed in 2010.6
The Cherry Valley Interchange project reconstructed the connection between Interstate 90 (Jane Addams Memorial Tollway) and I-39 in Rockford. The project started in 2008 and was completed on November 13, 2010. This work upgraded the trumpet interchange built in 1972 joining I-39/90 to utilize high speed ramps in all directions.7 An additional project widened the Tollway from Exit 3 (Rockton Road) to U.S. 20 Business (State Street) between 2007 and November 24, 2009.8
A long term project underway in south central Wisconsin, the I-39/90 Expansion Project, affected 45 miles of 1960s-era freeway along the I-39/90 overlap from the Illinois state line to U.S. 12/18 at Madison. Upgrades to the corridor included expansion of the freeway mainline to six overall lanes, reconfiguring 11 interchanges with substandard design elements, and additional expansion of I-39/90 to eight lanes from Wis 11 (Avalon Road) north to Wis 26. Construction ran from 2015 to 2021.10
The conversion of Exit 177 with Wis (Avalon Road) to a diverging diamond interchange created the first DDI in the state. Part of the South Segment at Beloit, a major upgrade started in Summer 2019 at the exchange joining I-39/90 with the south end of Interstate 43 and Wis 81. Work through Fall 2021 converted the previous cloverleaf interchange into a directional T for freeway to freeway movements and a DDI for Wis 81 leading west into Beloit.10