CC, this is how it works in the U.S.

Jail is for people who are being held without bond before their trial or if they can't make bond. It is also usually used for people who have to serve less than 1 year of time or 11 months 29 days.

Prison is for convicted criminals having to serve usually over 1 year of time.

So jail is going to have more non-violent offenders and low level criminals like those serving a small sentence for DUI or possesion or bad checks, shoplifting, small terms from violating probation.