One of my undergrad professors told us that Colorado has 63 counties (64 since we added the City & County of Broomfield in 2001) because the legislators wanted residents to have no more than a one day’s horseback ride to the county seat.
Source: Map from http://www.colorado.gov
I’ve never tried to verify that, but I wonder if that’s true, or if they just gave up by the time they reached the western slope. In Colorado, you can find a number of strange city/county arrangements, many caused by the geography of mountains and rivers.
For example, Redstone, Colorado, is located in Pitkin County. You might be able to make it over the mountains to the county seat in Aspen in a day’s horseback ride, but to drive from Redstone to Aspen, one goes through Carbondale.
Map modified from Wikimedia Commons. Place names roughly added.
From Basalt, you could have ridden a horse to the county seat of Eagle via Ruedi Reservoir and the Woods Lake road, but the best roads today lead through Glenwood Springs, then Glenwood Canyon.
Debeque is in Mesa County, but it’s separated by a canyon from the county seat in Grand Junction, so Garfield County takes care of some of Debeque’s needs while Mesa County takes care of parts of Garfield County.
I sometimes wonder why Colorado needs 64 counties while our mountainous neighbors have far fewer: Utah–29; Wyoming–23; New Mexico–33. But at this point, it seems as though the county configuration is unlikely to change.
States, Counties, & Statistically Equivalent Entities gives historical background on county formation in relation to the federal census.