Have county sizes changed much since the 1800s?

Question

Is it safe to assume that county sizes are about the same now as they were in the 19th century?

Answer 1

Yes, it is. Almost all counties in the United states were already established in the 1800s. The few states established since then generally followed the pattern established previously. Alaska's counties are an exception as they tend to be quite large, but not the largest in the country. Each of Hawaii's 5 main islands is a separate county, but they still fall within the usual size range.

Answer 2

Off the top of my head I would suggest that any boundary that is designated as the center of a river could change. For example the international border between the US and Mexico is the center of the Rio Grande river. If the river changes course the border changes, so the counties could change size.