What's got me rather confused is figuring out law enforcement organization during this time period. I've found that some cities had police by this time, and I've found that sometimes it was organized by Marshal-Sheriff-Deputies. I'm not sure whether I can justify a small town by, say, the 1870's having a small police department, or if they'd be under a sheriff or what. Then, I'm having trouble finding information about how either of these would have been organized at this time (particularly early police forces), such as in terminology and ranking.
I can find plenty on England, but I need sources about the US.