Tennessee has a lot of counties (and hence county jails), but two of the largest are Shelby County Jail and Davidson County Jail. CountyJail.net shares exclusive interviews of ex-inmates of these jails and many more.

County Jail vs. Prison
If you know somebody who is facing a serious criminal charge you should first discuss with their attorney whether they are facing time in a county jail or a state (or federal) prison facility.

County jails are where most people go who are charged with misdemeanors (which are much less serious than felonies). If you have been charged with a felony you may still end up at county jail, but the risk increases that you will be sent to prison.

When you turn on the TV and see a lot of violence in jail including fighting, rape, etc., this is depicting a prison setting, not a county jail. Since most inmates in county jail are serving less than a year they won't usually want to risk picking up more serious charges or being transferred to a prison (where they are much more likely to spend a multi-year sentence).

Largest county jails in Tennessee
The largest county jails in Tennessee are Shelby and Davidson (respectively). In these larger jails you tend to see more violence than in smaller facilities. Ex-inmates of the Davidson County Jail report that racial tensions run high and it is rare for whites and blacks to get along. Of course this isn't always the case, but it is something to be aware of if you are heading to the Davidson County Jail.

The advantage of a larger jail is that it's easier to blend in than a smaller jail. If you are in a jail with a hundred or less inmates it is very unlikely that you will be able to keep your charges to yourself or really have any privacy at all. Just try to get along the best you can. Stay out of other people's business and you shouldn't have any problems.