Only in these two states...

[Flint1979]

Nevada and Alaska.

Only two states that have their largest cities not connected via an Interstate

Las Vegas is on I-15

I should've worded that different.

Only states where the two largest cities (Reno and LV) not connected to each other via an interstate

Delaware as well.

Interestingly, the second largest city in Alaska keeps changing. In 2000, it was Juneau. In 2010, it was Fairbanks. The 2019 estimate puts it back in Juneau, with Fairbanks losing population since 2010 in absolute numbers. Fairbanks is connected to Anchorage via unsigned Interstate, but Juneau is not.

Juneau's competitiveness with Fairbanks for the #2 spot is only possible because the city and borough of Juneau is one entity.  Fairbanks only counts what's within the city limits; there is a much larger population in the remainder of the North Star Borough, whereas the Juneau "metro" is all within the city limits.  In other words, Fairbanks is a much more populous metropolitan area, Juneau is only #2 because of this "quirk" that they annexed the entire borough within which they are located.  This is much like Jacksonville (Duval Co.) or Virginia Beach (Princess Anne Co.), only there is basically wilderness outside of Juneau.  https://www.google.com/maps/place/Juneau,+AK/@58.4479638,-135.2585425,8.5z/data=!4m5!3m4!1s0x5400de6c6f6a3a8f:0x65ef25aae69f311!8m2!3d58.3019444!4d-134.4197221

Fairbanks North Star Borough is about the size of New Jersey in area while Juneau in area is a little bigger than Delaware in area. So it's about 3 or 4 times bigger in area.

[Revive 755]

Could have sworn that I saw the IH abbreviation on a sign or message board in Wisconsin.

Wisconsin would call everything "highway X" with no prefix.

As of today there are at least three temporary orange text construction signs using IH in Wisconsin:

* WB US 12 prior to I-43 (for construction on SB I-43)

* At least two in the Milwaukee area using IH 41 - US 45 for the construction north of the Zoo Interchange.

[Big John]

Could have sworn that I saw the IH abbreviation on a sign or message board in Wisconsin.

Wisconsin would call everything "highway X" with no prefix.

As of today there are at least three temporary orange text construction signs using IH in Wisconsin:

* WB US 12 prior to I-43 (for construction on SB I-43)

* At least two in the Milwaukee area using IH 41 - US 45 for the construction north of the Zoo Interchange.

WisDOT highway plans officially uses "IH" for interstate highway.  They aren't seen in the field besides contractor error or in this case, misdesign of the orange signs.

[ctkatz]

california and nevada

the only two to sign mile markers on the county level on the interstates.