:::I'm unaware of any law that would make such forms public domain.  notes that "Copyright protection under this title is not available for any work of the United States Government, but the United States Government is not precluded from receiving and holding copyrights transferred to it by assignment, bequest, or otherwise.";  defines its terms thusly: "A “work of the United States Government” is a work prepared by an officer or employee of the United States Government as part of that person’s official duties." State governments are not precluded from claiming copyright, and Compendium II: Copyright Office Practices, § 206.02 further adds that, "Works of the government of Puerto Rico are not considered to be U.S. Government works." It also says that "...the fact that a copyright may have been transferred to the U.S. Government is not determinative of its status.... Similarly, the fact that the work has been printed by the U.S. Government does not determine its copyright status." 

 :::In terms of federal court filings, court judgments are not subject to copyright under U.S. law whether these are federal, state or produced by other nations (no governmental edicts are). (Compendium II: Copyright Office Practices, § 206.01) Federal court filings are public information are public records, but that's not the same thing as being public domain. (See Wikipedia:Public domain#Public records). While court judgments are public domain, I'm unaware of any legislation that has made all federal court filings public domain. If a private citizen files a deposition, his words are available for scrutiny, but not necessarily for modification and reuse.