If you have researched the inmate's name in the Inmate Locator and there is no ID #, you may send the letter without the number. There are some facilities that do not have numbers for their inmates.
https://www.inmateaid.com/ask-the-inmate/how-do-i-send-an-inmate-a-letter-if-i-dont-know-their-id-number#answer
Accepted Answer Date Created: February 27,2013