The fair place to meet is Denver, CO — the city closest to the midpoint of Milwaukee and Portland. From the farther side that’s about 20 hr 34 min of driving.
Recommended midpoint
Denver, CO
From Milwaukee
19 hr 8 min
913 mi to Denver
From Portland
20 hr 34 min
981 mi to Denver
Milwaukee has the shorter trip; the split is off by about 1 hr 26 min. The alternatives below can even it out. Milwaukee and Portland are about 1,715 miles apart.
Milwaukee and Portland are about 1,715 miles apart by road. Split the difference and you arrive near Denver, the city closest to the halfway point between them. That puts roughly 19 hr 8 min of driving on the Milwaukee side and 20 hr 34 min on the Portland side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. Denver still makes a fair, central place for Milwaukee and Portland to converge, splitting the travel instead of asking one side to cross the country.
If Denver doesn't have what you're after, Salt Lake City and Omaha are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Milwaukee and Portland.
Denver is the capital and most populous city of the U.S. state of Colorado. Officially a consolidated city and county, it is located in the South Platte River valley on the western edge of the High Plains, and is just east of the Front Range of the Rocky… Read more →
Milwaukee is the most populous city in the U.S. state of Wisconsin. It is located on the western shore of Lake Michigan at the confluence of the Milwaukee, Menomonee, and Kinnickinnic Rivers. Read more →
Portland is the most populous city in the U.S. state of Oregon. Located in the Pacific Northwest at the confluence of the Willamette and Columbia rivers, it is the 28th-most populous city in the United States, sixth-most populous on the West Coast, and… Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.