Over 4,600 green card recipients resided in Oklahoma in 2019 (Statista). The applications of these recipients and all others, except those seeking asylum, are processed by the U.S. Citizenship and Immigration Services (USCIS). The USCIS is under the Department of Homeland Security (DHS), and the federal agency operates through its physical locations, website, and phone service.
As an immigration applicant, your interview is held at a field office of the USCIS. The number of field offices in a State varies. Instead of cities or States, the agency uses a system of Districts and Regions. Districts can have jurisdiction over counties present in multiple states. The Districts are divided into 4 regions: Northeast, Southeast, Central, and Western.