There are almost 3200 jails and local lock ups throughout the various states. The jails and local lock ups are part of the county government or are part of the city government. Many of the jails are under the control of the local sheriff. The jails and other local facilities hold individuals waiting for trial or inmates serving short sentences. In Maryland, if your sentence is under 18 months, you usually will serve your time in the county detention center.. With almost 20,000 inmates, Los Angeles County has the biggest jail population in the United States. Dangerously overcrowded state prison systems, such as California, are sending inmates to local jails. The inmate transfers are overcrowding the jails and other local lock ups.