I haven’t read the Fischel book (and taking the deplorable lack of posting here as indicative of limited time for extracurriculars, I won’t be any time soon) but I did manage to put together a quick look at county sizes in the US. Here’s a table of average and median county sizes for the US excluding Alaska, which has such low population density that much of its territory is not divided into jurisdictions below the state level.
The table is color-coded: red = South (get it?), blue = North (obviously), green = Midwest (because farms), orange = West (sunsets), white = Hawaii and Texas (because they’re special). Let’s sort things out by region and see if any patterns show up.
The South seems to generally have the smallest counties. In the rest of the country, there are only 3 states with average county size under 500 square miles (NJ, RI, and IN, the most southern of northern states), while in the South there are 5. States that are further west within the south seem to have larger counties. Georgia is famous for its small, numerous counties, which help frustrate regional planning efforts. Virginia has the smallest average save tiny Rhode Island because many cities in Virginia exist as their own entity outside of any county.
The North and Midwest have similar county sizes, with an average of around 800 square miles in both. It should be noted that in legal terms, counties don’t exist in Connecticut or Rhode Island at all. County government has been completely abolished and the counties serve only as districts of services administered by the state. Massachusetts has a strange situation, having formally abolished 8 of its 14 counties.
The West is typified by much larger counties, with an average of almost 2,900 square miles. Arizona’s and Nevada’s average counties are larger than the 3 smallest states, and the largest county, San Bernardino, is larger than the 9 smallest states.
The West could be further subdivided into the Mountain West/Pacific Northwest and the Southwest. This division splits California in half, assigning 12 counties to SoCal (San Luis Obispo, Kern, Mono, Inyo, San Bernardino, Santa Barbara, Ventura, Los Angeles, Orange, Riverside, San Diego, Imperial) and the rest to NorCal. The Mountain West/Pacific Northwest has an average county size of about 2,250 square miles while the Southwest has the true giants, averaging over 4,700 square miles.
Based on the county sizes of the South, North, and Midwest, it seems that the governing land survey system had relatively little impact on county sizes. The North and Midwest in particular ended up with almost the same average size, despite the former being almost entirely metes and bounds and the latter being almost entirely US Public Land Survey System (USPLSS).
My guess is that there were two factors that influenced county size: suitability of land for frontier industry like farms and mining, and the types of transportation available at the time the county was established.
The first factor was also proposed to impact suburbanization patterns, and it is probably the easiest to see. If the land was not suitable for agriculture or mining, it would not be densely settled, and there would be no need to create new counties. This is why Maine has by far the largest county size in the North: its vast northern woods were never converted into small farms because of unfavorable climate. This also explains why Michigan, Minnesota, North Dakota, and South Dakota have the largest county sizes in the Midwest; they also contain large areas that were unsuitable for agriculture.
As has been widely discussed elsewhere, the suitability of the US for agriculture decreases as you move west towards the Great Plains and Mountain West. Looking at a map of counties in Nebraska or Colorado, one can almost visualize the wave of regular square USPLSS-centric counties marching westward, breaking up on the Sand Hills, and finally dying at in the dry steppes at the foot of the Rockies.
Texas is special because it straddles several regions. Its eastern counties, while not small, follow irregular borders. Further west, there are many almost regular square counties of about 900 square miles. West of the Pecos, Texas counties are larger and more like the Southwest.
The second factor, the time the county was created, can be seen in places like California. Many of Northern California’s small counties date to the Gold Rush, before there were even any railroads to speak of in the state. This is likely due to the need to have law enforcement and administrative services within a reasonable amount of traveling time. For example, Alpine County, on the east side of the Sierra Crest, was created in 1864 during a silver boom. Even today, there are only 5 roads into Alpine County, and 2 are closed during the winter with another 2 frequently affected by snow, and the last leading into Nevada. The relative isolation caused by very poor transportation infrastructure necessitated small counties, in order to have functional government.
In contrast, Southern California remained relatively unpopulated until the 20th century. At the time of its creation, Alpine County had a larger population than LA County or SB County. By the time LA started to boom, though, railroads were well established, autos were in development, and long distance communication by telegraph was much easier.
Simply put, there’s no longer any compelling need to create new counties. The Southwest’s large counties, established to govern vast empty areas, remain as such as they grow into some of America’s largest urbanized areas. This accident of history results in some fortuitous circumstances, because it makes it possible to have significant regional impacts by acting at the county level. A worthwhile infrastructure project on the east coast might involve multiple counties if not multiple states; in San Francisco it will almost certainly involve multiple counties; in SoCal, Las Vegas, or Phoenix, the county is usually enough.