Q. Who do I serve if I am filing a FOIA lawsuit against the U.S. Customs & Border Patrol?
A. Service of process in federal matters is governed by Rule 4 of the Federal Rules of Civil Procedure. Note that subsection (i) addresses suits against the United States and its agencies. You might also wish to consult the local rules of the district court in which you file the suit. As an example, see the local rules for the U.S. District Court for the District of Columbia. Additionally, section 5.42 of title 6 of the Code of Federal Regulations provides information about the service of summonses and complaints against the U.S. Department of Homeland Security.
Guidance for pro se litigants is available from most federal district courts. The U.S. District Court for the District of Columbia, for example, has published this handbook about how to file suits.