I grew up in Iowa and learned in the 8th grade that we had 99. The county size was determined by how far a horse and carriage could travel in one day and this was supposed to be roughly the distance from the county seat to the farthest part of the county. Interestingly enough, one county is twice the size of the others. If they had cut it in half, Iowa would have an even hundred. I guess even back then they just had to stay with two digits.
Counties vary widely by population.
Los Angeles County has over nine million people, while Loving County in Texas only has 141. Ms. Lyday recounted that the vital records maintained at the county level include birth and death records, marriage, voting, elections and some educational records. In the justice system, the counties are responsible for law enforcement, prosecution and defense, criminal and civil cases, most of the jails, and the records of alimony and child support. Counties are also the place for records dealing with land such as recording the deeds, surveys, building permits, business licensing, assessments and taxation. They also are in charge of planning, zoning, roads and traffic, transportation, emergency services such as 911 and disaster response.