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American Architects Directories:
Address listed in 1956 American Architects Directory
Biographical listing in 1962 American Architects Directory
Address listed in 1970 American Architects Directory
Biographical Directories:
Biographical entry and list of works at the Washington State Department of Archaeology & Historic Preservation web site http://www.dahp.wa.gov/learn-and-research/architect-biographies/day-w-hilborn
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The American Institute of Architects Archives
Membership file contains membership application, request for emeritus (retired) status.
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