That would depend upon whether it was a published or unpublished work and, if published, who the publisher was for the edition you want to copy, and whether the author assigned some or all of his rights to the publisher or anyone else.
Furthermore, some of his literature was created while an employee of others, making the employer the legal "author" of those works. If the work was created as part of his duties while employed by the U.S. government, then those works are not copyrighted.
Absent any written transfer of rights, if any, his heirs at law would own them.
Keith Gordon Irwin has written: 'Man learns to measure' -- subject(s): History, Juvenile literature, Weights and measures
Michael Irwin has written: 'Henry Fielding: the tentative realist' -- subject(s): Criticism and interpretation, Realism in literature 'Striker' 'Reading Hardy's landscapes' -- subject(s): Settings, Landscape in literature, Technique, Description (Rhetoric), Setting (Literature), In literature, Landscape, History
Frank Irwin has written: 'Heraldic bookplates'
Gregor Irwin has written: 'The macroeconomics of the Mexican crisis'
Irwin Epstein has written: 'Clinical data-mining'
Alphonso Irwin has written: 'Dental laws condensed'
John B. Irwin has written: 'L'arthrite'
Thomas Caulfield Irwin has written: 'Versicles'
Fred C. Irwin has written: 'Mesabi story'
Harriet Sibyl Irwin has written: 'Nevada Hattie'
Paul P. Irwin has written: 'Interstitial cystitis'
Michael John Irwin has written: 'The Lawyer's Pocketbook'