That depends, it's just under 80 miles on I-90 from the ID/WA border to the ID/MT border up north in the panhandle. Down south it is 408 miles on I-84
Arkansas is approximately 240 miles wide from its eastern border with Tennessee to its western border with Oklahoma.
The state of Montana is approximately 630 miles wide from its eastern border with North Dakota to its western border with Idaho. This measurement is taken from the widest point of the state, which is near the city of Plentywood in the east to the city of Trout Creek in the west. Montana is the fourth-largest state in the US by land area, covering over 147,000 square miles.
At its narrowest point Idaho is 50 miles wide.
Vermont is 37 miles wide at the southern border with Massachusetts
Illinois is about 390 miles wide from the eastern border with Indiana to the western border with Iowa.
It is about 70 miles from the eastern to western border of New Jersey.
The Texas-Mexican border is approximately 1254 sq. miles.
Hells Canyon is a ten mile wide canyon located along the border of eastern Oregon and western Idaho.
Montana is 630 miles wide.
The widest point of Maryland occurs at its northern border with Pennsylvania. The measured width there is about 250 miles.
630 miles wide