The National Register of Historic Places recognizes buildings, structures, objects, sites, and districts of national, state, or local historic significance across the United States. Out of over 90,000 National Register sites nationwide,Oregon is home to more than 2,000 NRHP listings.
Over one-fourth of the NRHP listings in the state are found in Multnomah County. In turn, the large majority (over 90%) of Multnomah's NRHP sites are situated within the city of Portland.
^These counts are based on entries in the National Register Information Database as of April 24, 2008 and new weekly listings posted since then on the National Register of Historic Places web site. There are frequent additions to the listings and occasional delistings and the counts here are approximate and not official. New entries are added to the official Register on a weekly basis. Also, the counts in this table exclude boundary increase and decrease listings which only modify the area covered by an existing property or district, although such increases and decreases carry a separate National Register reference number.
^Several historic resources within Multnomah County are included on multiple area lists:
^Oregon Parks and Recreation Department, Oregon Historic Sites Database, retrieved July 26, 2014. Note that a simple count of National Register records in this database returns a slightly higher total than actual listings, due to duplicate records. A close reading of detailed query results is necessary to arrive at the precise count.