Longest state highways entirely within one county

[iowahighways]

Iowa's longest is IA 62, which spends all of its 20 miles in Jackson County. Runners-up: IA 117 (18 miles in Jasper County), IA 415 (17 miles in Polk County), I-880 (17 miles in Pottawattamie County), IA 100 (16 miles in Linn County), and IA 127 (16 miles in Harrison County).

[Life in Paradise]

Not very long for Indiana. The southern IN 11 is 29.8 miles and entirely in Harrison County.

The southern SR 11 starts in Floyd County before heading south into Harrison County. Now nearby, SR 337 (the southern segment) does stay entirely in Harrison County and goes for 22 miles.

Indiana SR 69 is entirely in Posey County, and is 35.6 miles long.  Is does share about 5 miles with IN SR 62 through Mt. Vernon.

[bulldog1979]

For Michigan, I believe the answer is M-142 in Huron County at 39.2 miles

[gonealookin]

Nevada:

If we allow state highways that end at a state line and continue into the next state, it's Nevada 140 in Humboldt County, part of the Winnemucca to the Sea Highway, starting at US 95 and ending at the NV/OR border, where it continues as Oregon 140.  That one measures 110.057 miles.

For highways that don't end at a state line, the winner is Nevada 305 in Lander County.  That one runs 87.656 miles from US 50 near Austin to Nevada 304 in Battle Mountain.

[paulthemapguy]

I'm guessing that Illinois's answer might be Illinois 81, which is 25.78 miles long and completely within Henry County.

[DandyDan]

For Nebraska, I would guess this is NE 250, which is 48.64 miles and all in Sheridan County.

[jeffandnicole]

NJ...looks like it's NJ 17 at 27.2 miles, entirely in Bergan County.