In most cases you will end up using a local bail company...
Locate the state, then the city or county where you think they are being held.
Call the jail or search for information about bail for your local jail by going to your individual jail or prison page on jailexchange. Confirm that the person has been booked into jail, that bail is allowed, and find out what they recommend for the quickest way to get the person released.
In most cases you will end up using a local bail company that is familiar with the jail’s procedures and they will assist you in this process.
To find your jail's bail policies, research eligibility for bail, or to search for an inmate or arrestee, begin here: