The Federal Bureau of Prisons maintains a map of current halfway house locations that you can use to find the location of a specific halfway house. Prison officials are generally responsible for choosing a halfway house for prisoners.
Halfway houses, also known as residential re-entry centers, are part of the prison system. Prisoners generally enter them near the end of their sentences, but they are still inmates and have limited freedom. Since these centers are still part of the prison system, government officials are responsible for recommending them and handling the placement and transfer of the prisoner. In general, the team overseeing the prisoner makes the recommendation for transfer to a halfway house, then sends the information to a residential re-entry management office. The workers there choose a house and negotiate the placement with the company or agency that runs it.
Inmates who are facing homelessness after being released can talk to their unit team or parole officer to find help. Some inmates may be eligible for a housing voucher program to help them find a place to live. Some faith-based organizations also work with prisoners to find safe and affordable housing. Prisoners can also try to access informal halfway houses. These are often focused on substance abuse treatment or similar issues. You can often find them through counselors or organizations that treat mental illness and addiction.