{{short description|Highway in Wisconsin}} {{Use American English|date=May 2025}} {{Use mdy dates|date=January 2025}} {{One source|date=November 2021}}{{Infobox road |state=WI |type=WI |route=78 |length_mi=92.83 |length_ref= <ref name="WH1">{{cite web | last = Bessert | first = Chris | title =Wisconsin Highways: Highways 70-79 (Highway 78) | work =Wisconsin Highways | url =http://www.wisconsinhighways.org/listings/WiscHwys70-79.html#STH-078 | accessdate = 2007-03-20}}</ref> |map={{maplink-road|from=Wisconsin Highway 78.map}} |map_custom=yes |map_notes=WIS 78 highlighted in red |direction_a=South |terminus_a={{Jct|state=IL|IL|78}} in [[Gratiot, Wisconsin|Gratiot]] |junction= *{{Jct|state=WI|US|18|US|151}} in [[Mount Horeb, Wisconsin|Mount Horeb]] *{{Jct|state=WI|US|14}} in [[Black Earth, Wisconsin|Black Earth]] *{{Jct|state=WI|US|14|WI|19}} in [[Mazomanie, Wisconsin|Mazomanie]] *{{Jct|state=WI|US|12|WI|60}} in [[Sauk City, Wisconsin|Sauk City]] |direction_b=North |terminus_b={{Jct|state=WI|I|39|I|90|I|94}} in [[Portage, Wisconsin|Portage]] |counties=[[Lafayette County, Wisconsin|Lafayette]], [[Iowa County, Wisconsin|Iowa]], [[Green County, Wisconsin|Green]], [[Dane County, Wisconsin|Dane]], [[Sauk County, Wisconsin|Sauk]], [[Columbia County, Wisconsin|Columbia]] |previous_type=WI |previous_route=77 |next_type=WI |next_route=79 }} '''State Trunk Highway&nbsp;78''' (often called '''Highway 78''', '''STH-78''' or '''WIS&nbsp;78''') is a [[state highway (US)|state highway]] in the U.S. state of [[Wisconsin]]. It runs north–south in south central Wisconsin from the Illinois border near [[Gratiot, Wisconsin|Gratiot]] to [[Portage, Wisconsin|Portage]].

==Route description== WIS&nbsp;78 begins at the Illinois state line, continued from [[Illinois Route 78]] (IL&nbsp;78). It enters [[Gratiot, Wisconsin|Gratiot]], where it merges with [[Wisconsin Highway 11|WIS&nbsp;11]] and leaves Gratiot. WIS&nbsp;78 turns north, and [[concurrency (road)|runs concurrently]] with [[Wisconsin Highway 81|WIS&nbsp;81]] in [[Argyle (village), Wisconsin|Argyle]] before turning to go north in the [[Driftless Area]]. WIS&nbsp;78 passes through [[Blanchardville, Wisconsin|Blanchardville]]. The highway runs concurrently with [[Wisconsin Highway 39|WIS&nbsp;39]] for less than a quarter of a mile (0.4&nbsp;km) before the two highways part ways, and WIS&nbsp;78 passes through [[Daleyville, Wisconsin|Daleyville]] and enters [[Mount Horeb, Wisconsin|Mount Horeb]], crosses [[U.S. Route 18 in Wisconsin|US&nbsp;18]]/[[U.S. Route 151|US&nbsp;151]], and meets [[Wisconsin Highway 92|WIS&nbsp;92]] at its western terminus.

WIS&nbsp;78 continues north out of Mount Horeb through the Driftless Area. It enters [[Black Earth, Wisconsin|Black Earth]] and merges with [[U.S. Route 14 in Wisconsin|US&nbsp;14]] west and the routes run concurrently, leaving Black Earth. WIS&nbsp;78 turns north. [[Wisconsin Highway 19|WIS&nbsp;19]] begins at this intersection and the two routes run concurrently for a mile, before WIS&nbsp;19 turns to go east. WIS&nbsp;78 runs parallel to the [[Wisconsin and Southern Railroad]] for several miles.

The highway merges with [[U.S. Route 12 in Wisconsin|US&nbsp;12]] and crosses the [[Wisconsin River]], entering [[Sauk City, Wisconsin|Sauk City]] before it turns to go north, now running concurrently with [[Wisconsin Highway 60|WIS&nbsp;60]]. WIS&nbsp;60 turns to go east and WIS&nbsp;78 continues out of Sauk City, paralleling the Wisconsin River for several miles. It merges with [[Wisconsin Highway 113|WIS&nbsp;113]], creating a [[wrong-way concurrency]] with WIS&nbsp;113 south and WIS&nbsp;78 north, and vice-versa. In [[Merrimac, Wisconsin|Merrimac]], WIS&nbsp;113 turns to cross [[Lake Wisconsin]] with the [[Merrimac Ferry]]. The route continues for {{convert|12|mi|km}} before ending at an interchange with [[Interstate&nbsp;39]] (I-39) and [[Interstate 90 in Wisconsin|I-90]]/[[Interstate 94 in Wisconsin|I-94]]. At the interchange, the roadway continues as I-39.

==History== In the 1920s, WIS&nbsp;78 was originally located on the [[Door County, Wisconsin|Door County]] Peninsula on what is now [[Wisconsin Highway 57|WIS&nbsp;57]].{{citation needed|date=December 2023}}

In 1963, the segment of WIS&nbsp;78 from the new I-90/I-94 freeway interchange south of Portage northerly to [[Wisconsin Highway 33|WIS&nbsp;33]] was improved to a four-lane divided facility. A year later, this four-lane divided highway (and the WIS&nbsp;78 designation with it) was extended northerly across the Wisconsin River then bypassing Portage to the west before merging into the existing two-lane route of [[U.S. Route 51 in Wisconsin|US&nbsp;51]] north of the city. The entire four-lane divided portion of WIS&nbsp;78 from I-90/I-94 northerly to US&nbsp;51 was shown as a full freeway with interchange beginning with the 1966 official state highway map, so it can be assumed the conversion to freeway occurred about this time (c.1965). In more recent decades, the short segment of WIS&nbsp;78 freeway was the only portion of the route from I-90/I-94 at Portage northerly past Wausau that was not signed as part of US&nbsp;51, although signs along the route did indicate "To US&nbsp;51". Then in 1996, US&nbsp;51 from Rothschild (south of Wausau) southerly to Portage was concurrently designated as [[Interstate 39|I-39]] and to connect this new Interstate route with nearby I-90/I-94, the entire WIS&nbsp;78 freeway from US&nbsp;51 north of Portage to I-90/I-94 was redesignated as part of I-39, with WIS&nbsp;-78 losing approximately {{convert|8|mi|km|spell=in}} of length in the process.{{citation needed|date=December 2023}} {{Clear}}

==Major intersections== {{Jcttop}} {{WIint |county=Lafayette |cspan=5 |town=Gratiot |mile=0.0 |road={{Jct|state=IL|IL|78|dir1=south|city1=Warren}} |notes=Continuation into Illinois }} {{WIint |location=Gratiot |lspan=2 |type=concur |mile=5.8 |road={{Jct|state=WI|WI|11|dir1=west|city1=Shullsburg}} |notes=Western end of WIS 11 concurrency }} {{WIint |type=concur |mile=6.2 |road={{Jct|state=WI|WI|11|dir1=east|city1=Monroe}} |notes=Eastern end of WIS 11 concurrency }} {{WIint |location_special=[[Argyle (village), Wisconsin|Argyle]] |lspan=2 |type=concur |mile=20.1 |road={{Jct|state=WI|WI|81|dir1=west|city1=Darlington}} |notes=Western end of WIS 81 concurrency }} {{WIint |type=concur |mile=20.4 |road={{Jct|state=WI|WI|81|dir1=east|city1=Monroe}} |notes=Eastern end of WIS 81 concurrency }} {{Jctco|state=WI|county=Iowa}} {{WIint |county=Green |cspan=2 |town=York |ctdab=Green |lspan=2 |type=concur |mile=32.5 |road={{Jct|state=WI|WI|39|dir1=west|city1=Mineral Point}} |notes=Western end of WIS 39 concurrency }} {{WIint |type=concur |mile=32.7 |road={{Jct|state=WI|WI|39|dir1=east|city1=New Glarus}} |notes=Eastern end of WIS 39 concurrency }} {{WIint |county=Dane |cspan=6 |location=Mount Horeb |lspan=2 |type=concur |mile=45.7 |road={{Jct|state=WI|US|18|US|151|city1=Madison|city2=Dodgeville}}<br>{{Jct|state=WI|US-Bus|18|dab1=Mount Horeb|dir1=east|US-Bus|151|dab2=Mount Horeb|dir2=east}} |notes=US 151 exit 65; southern end of Business US 18 / Business US 151 concurrency }} {{WIint |type=concur |mile=47.5 |road={{Jct|state=WI|US-Bus|18|dab1=Mount Horeb|dir1=east|US-Bus|151|dab2=Mount Horeb|dir2=north|CTH|ID|name3=Springdale Street|WI|92|dir4=south|name4=8th Street}} |notes=Roundabout; northern end of Business US 18 / Business US 151 concurrency }} {{WIint |location=Black Earth |type=concur |mile=57.6 |road={{Jct|state=WI|US|14|dir1=east|city1=Madison}} |notes=Southern end of US 14 concurrency }} {{WIint |location=Mazomanie |type=concur |mile=59.9 |road={{Jct|state=WI|US|14|dir1=west|WI|19|dir2=north|city1=Spring Green}} |notes=Northern end of US 14 concurrency; southern end of WIS 19 concurrency }} {{WIint |town=Mazomanie |type=concur |mile=61.3 |road={{Jct|state=WI|WI|19|dir1=east|city1=Waunakee}} |notes=Northern end of WIS 19 concurrency }} {{WIint |town=Roxbury |type=concur |mile=67.8 |road={{Jct|state=WI|US|12|dir1=east|city1=Madison}} |notes=Eastern end of US 12 concurrency }} {{WIint |county=Sauk |cspan=4 |location=Sauk City |type=concur |mile=68.4 |road={{Jct|state=WI|US|12|dir1=west|WI|60|dir2=west|name2=Phillips Boulevard}} |notes=Western end of US 12 concurrency; southern end of WIS 60 concurrency }} {{WIint |location=Prairie du Sac |type=concur |mile=70.0 |road={{Jct|state=WI|WI|60|dir1=east|name1=Prairie Street}} |notes=Northern end of WIS 60 concurrency }} {{WIint |town=Merrimac |type=concur |mile=77.3 |road={{Jct|state=WI|WI|113|dir1=north|city1=Baraboo}} |notes=Western end of WIS 113 concurrency }} {{WIint |location=Merrimac |type=concur |mile=79.9 |road={{Jct|state=WI|WI|113|dir1=south|extra=ferry|location1=[[Merrimac Ferry]]}} |notes=Eastern end of WIS 113 concurrency }} {{WIint |county=Columbia |town=Caledonia |ctdab=Columbia |mile=92.83 |road={{Jct|state=WI|I|39|dir1=south|I|90|I|94|city1=Wisconsin Dells|city2=Madison}}<br>{{Jct|state=WI|I|39|dir1=north|city1=Portage}} |notes=Roadway continues as northbound I-39 }} {{Jctbtm|keys=concur}}

==See also== *{{portal-inline|U.S. Roads}}

==References== {{reflist}}

==External links== {{Attached KML|display=title,inline}} *{{Commons category-inline|Wisconsin Highway 78}}

[[Category:State highways in Wisconsin|078]] [[Category:Transportation in Lafayette County, Wisconsin]] [[Category:Transportation in Iowa County, Wisconsin]] [[Category:Transportation in Green County, Wisconsin]] [[Category:Transportation in Dane County, Wisconsin]] [[Category:Transportation in Sauk County, Wisconsin]] [[Category:Transportation in Columbia County, Wisconsin]]