You need to know the state they are in to begin. Most immigrant arrestees are held in ICE facilities. Click this [Immigration Detainee Locator](https://locator.ice.gov/odls/homePage.do) to locate them
https://www.inmateaid.com/ask-the-inmate/how-do-i-locate-an-immigrant-who-has-been-arrested#answer
Accepted Answer Date Created: March 14,2016