|Virtually no petroleum was used in agriculture in 1870 and even into the 1930s tractors were far from ubiquitous on the farm.|
For example, what are the carrying capacities of the communities Kates Store and Pray Church in a post-oil economy?
Looking at Census data it becomes clear that the population density in south-central Michigan's rural, agricultural areas flat-lined starting in 1870 at about forty-eight people per square mile. That population density remained essentially unchanged until the start of World War II some seventy year later.
What does forty-eight people per square mile look like?
A square mile holds 640 acres.
If the population is in maintenance mode then we are talking two children per family in round numbers.
Forty-eight people divided by four per family means that twelve families will populate the square mile. It also means that the average farm size will be a bit more than fifty acres.
That works out well because a single family that relies on horse power can farm about forty acres. Fifty acres is forty acres with a nice woodlot or permanent pasture.
Or if we are talking three-generation households we are talking six-per-household and eight families per square mile. That noodles out to eighty acres per household so there need be an emphasis on low-labor/acre crops or a system of agriculture that levels the labor demands across the year.
It should be obvious that these numbers only apply to south-central Michigan's climate and soil but the same analysis could be done for any group of counties in the United States. Wikipedia's standard format for reports on "Counties" includes census data.