State Trunk Highway 78
WIS 78 highlighted in red
Route information
Maintained by WisDOT
Length	92.83 mi[1] (149.40 km)
Major junctions
South end	IL 78 in Gratiot
Major intersections	US 18 / US 151 in Mount 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
Country	United States
State	Wisconsin
Counties	Lafayette, Iowa, Green, Dane, Sauk, Columbia
Highway system
Wisconsin State Trunk Highway System Interstate US State Scenic Rustic
← WIS 77 → WIS 79

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 the Illinois border near Gratiot to Portage.

Route description

WIS 78 begins south of Portage at an interchange with Interstate 39 (I-39) and I-90/I-94. The highway merges into a two-lane road and parallels the Wisconsin River. After 12 miles (19 km), the highway passes through Merrimac, where WIS 113 merges with WIS 78 for a few miles before it turns north toward Baraboo. WIS 78 continues southwest following the Wisconsin River. It enters Prairie du Sac and merges with WIS 60 as it enters Sauk City. WIS 78 merges with US Highway 12 (US 12) east, and WIS 60 merges with US 12 west. WIS 78 runs concurrently with US 12 for about half a mile. This concurrency crosses the Wisconsin River. After half a mile, WIS 78 turns to go south. It meets up with WIS 19, and the two highways run concurrently for a mile. WIS 19 ends at US 14, and WIS 78 merges with US 14 and the two highways run concurrently for a couple miles, where the concurrency enters Black Earth. WIS 78 turns to go south. It runs through the Driftless Area before entering Mount Horeb, where it meets WIS 92 at its western terminus and crosses US 18 and US 151.

The highway continues south out of Mount Horeb and passes through Dalyville. The highway runs concurrently with WIS 39 for less than a quarter of a mile before the two highways part ways. The highway then passes through Blanchardville. In Argyle, WIS 78 runs concurrently with WIS 81 for half of a mile before turning to go south. The highway merges with WIS 11 and enters Gratiot, where WIS 78 turns south. WIS 78 terminates at the Wisconsin–Illinois state line where it meets Illinois Route 78 (IL 78).

History

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

In 1963, the segment of WIS 78 from the new I-90/I-94 freeway interchange south of Portage northerly to WIS 33 was improved to a four-lane divided facility. A year later, this four-lane divided highway (and the WIS 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 WIS 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 WIS 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 I-39 and to connect this new Interstate route with nearby I-90/I-94, the entire WIS 78 freeway from US 51 north of Portage to I-90/I-94 was redesignated as part of I-39, with WIS -78 losing approximately eight miles (13 km) 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
		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
		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
		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
		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

See also

•  U.S. Roads portal

References

External links

• Media related to Wisconsin Highway 78 at Wikimedia Commons