Wisconsin Highway 78

State Trunk Highway 78
State Trunk Highway 78
Route information
	Maintained by WisDOT
Length	92.83 mi (149.40 km)
Major junctions
South end	IL 78 in Gratiot
	US 18 / US 151 in Mt. Horeb; US 14 in Black Earth; US 14 / WIS 19 in Mazomanie; US 12 / WIS 60 in Sauk City;
North end	I-39 / I-90 / I-94 in Portage
Location
Counties	Lafayette, Iowa, Green, Dane, Sauk, Columbia
Highway system

State Trunk Highway 78 (often called Highway 78, STH-78 or WIS 78) is a state highway in the U.S. state of Wisconsin. It runs north–south in south central Wisconsin from Portage to the Illinois border near Gratiot.

History[]

In the 1920s, Highway 78 was originally located on the Door County Peninsula on what is now Highway 57.

In 1963, the segment of STH-78 from the new I-90/I-94 freeway interchange south of Portage northerly to Highway 33 was improved to a four-lane divided facility. A year later, this four-lane divided highway (and the STH-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 US 51 north of the city. The entire four-lane divided portion of STH-78 from I-90/I-94 northerly to US-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 STH-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-51, although signs along the route did indicate "TO US-51." Then in 1996, US-51 from Rothschild (south of Wausau) southerly to Portage was concurrently designated as Interstate 39 and to connect this new Interstate route with nearby I-90/I-94, the entire STH-78 freeway from US-51 north of Portage to I-90/I-94 was redesignated as part of I-39, with STH-78 losing approximately eight miles of length in the process.

Major intersections[]

County	Location	mi	km	Destinations	Notes
Lafayette	Town of Gratiot	0.0	0.0	IL 78 south – Warren	Continuation into Illinois
	Gratiot	5.8	9.3	WIS 11 west – Shullsburg	Western end of WIS 11 concurrency
	Gratiot	6.2	10.0	WIS 11 east – Monroe	Eastern end of WIS 11 concurrency
	Argyle	20.1	32.3	WIS 81 west – Darlington	Western end of WIS 81 concurrency
	Argyle	20.4	32.8	WIS 81 east – Monroe	Eastern end of WIS 81 concurrency
Iowa	No major junctions
Green	Town of York	32.5	52.3	WIS 39 west – Mineral Point	Western end of WIS 39 concurrency
Green	Town of York	32.7	52.6	WIS 39 east – New Glarus	Eastern end of WIS 39 concurrency
Dane	Mount Horeb	45.7	73.5	US 18 / US 151 – Madison, Dodgeville Bus. US 18 east / Bus. US 151 east	US 151 exit 65; southern end of Business US 18 / Business US 151 concurrency
	Mount Horeb	47.5	76.4	Bus. US 18 east / Bus. US 151 north / CTH-ID (Springdale Street) / WIS 92 south (8th Street)	Roundabout; northern end of Business US 18 / Business US 151 concurrency
	Black Earth	57.6	92.7	US 14 east – Madison	Southern end of US 14 concurrency
	Mazomanie	59.9	96.4	US 14 west / WIS 19 north – Spring Green	Northern end of US 14 concurrency; southern end of WIS 19 concurrency
	Town of Mazomanie	61.3	98.7	WIS 19 east – Waunakee	Northern end of WIS 19 concurrency
	Town of Roxbury	67.8	109.1	US 12 east – Madison	Eastern end of US 12 concurrency
Sauk	Sauk City	68.4	110.1	US 12 west / WIS 60 west (Phillips Boulevard)	Western end of US 12 concurrency; southern end of WIS 60 concurrency
	Prairie du Sac	70.0	112.7	WIS 60 east (Prairie Street)	Northern end of WIS 60 concurrency
	Town of Merrimac	77.3	124.4	WIS 113 north – Baraboo	Western end of WIS 113 concurrency
	Merrimac	79.9	128.6	WIS 113 south – Merrimac Ferry	Eastern end of WIS 113 concurrency
Columbia	Town of Caledonia	92.83	149.40	I-39 south / I-90 / I-94 – Wisconsin Dells, Madison I-39 north – Portage	Roadway continues as northbound I-39
1.000 mi = 1.609 km; 1.000 km = 0.621 mi Concurrency terminus