Owned by state government

Mortonville Bridge (Chester County, Pennsylvania)
Morven (Mercer County, New Jersey)
Moswetuset Hummock (Norfolk County, Massachusetts)
Mounds State Park (Madison County, Indiana)
Mount Baker Ridge Tunnel (King County, Washington)
Mount Greylock Summit Historic District (Berkshire County, Massachusetts)
Mount Hope Bridge (Unspecified County, Rhode Island)
Suspension bridge over Mount Hope Bay on RI 114 in Bristol
Mount Philo State Park (Chittenden County, Vermont)
Mount Pleasant Armory (Westmoreland County, Pennsylvania)
Mount Pulaski Courthouse (Logan County, Illinois)
Mount St. Gertrude Academy (Boulder County, Colorado)
Mount Tom Tower (Litchfield County, Connecticut)
Mount Tremper Fire Observation Station (Ulster County, New York)
Mount Zion Covered Bridge (Washington County, Kentucky)
Mountain Avenue Station (Essex County, New Jersey)
Mountain Station (Essex County, New Jersey)
Mt. Bleak--Skye Farm (030-0283) (Fauquier County, Virginia)
Mt. Nebo State Park-Pavilion (Yell County, Arkansas)
Mud River Covered Bridge (Cabell County, West Virginia)
Murray Hill Station (Union County, New Jersey)
Murray State University Historic Buildings (Calloway County, Kentucky)
Murrell Home (Cherokee County, Oklahoma)
Muskingum River Lock No. 10 And Canal (Muskingum County, Ohio)
My Old Kentucky Home (Nelson County, Kentucky)
Naaman's Creek School (New Castle County, Delaware)
Names Hill (Lincoln County, Wyoming)
Narrows Bridge (Parke County, Indiana)
Burr arch-truss bridge over sugar creek on old narrows road
Natchaug Forest Lumber Shed (Windham County, Connecticut)
Nation Ford Fish Weir (York County, South Carolina)
National Town and Country Club (Cuyahoga County, Ohio)
Natural Bridge Battlefield (Leon County, Florida)
Natural History Building (Champaign County, Illinois)
Natural History Museum (Los Angeles County, California)
Navajo Steel Arch Highway Bridge (Coconino County, Arizona)
Steel arch bridge over Colorado River on Alt US 89
Naval and Marine Corps Reserve Center (Hinds County, Mississippi)
Navesink Light Station (Monmouth County, New Jersey)
Neary-Rodriguez Adobe (Santa Cruz County, California)
Nebraska Governor's Mansion (Lancaster County, Nebraska)
Nebraska State Capitol (Lancaster County, Nebraska)
Nebraska State Historical Society Building (Lancaster County, Nebraska)
Nelson Hall (Portage County, Wisconsin)
Three-story brick dormitory built in Prairie School style
Nelson Ranch (Yolo County, California)
Netherwood Station (Union County, New Jersey)
Nevada State Capitol (Carson City, Nevada)
Nevada State Printing Office (Carson City, Nevada)
New Brighton Village Hall (Richmond County, New York)
New Brunswick Station (Middlesex County, New Jersey)
New Castle Armory (Lawrence County, Pennsylvania)
New Castle County Court House (New Castle County, Delaware)
New Discovery State Park (Caledonia County, Vermont)
New Echota (Gordon County, Georgia)
New Enterprise Public School (Bedford County, Pennsylvania)
New Fort Brady (Chippewa County, Michigan)
New Haven County Courthouse (New Haven County, Connecticut)
New Haven Junction Depot (Addison County, Vermont)
New Haven Railroad Danbury Turntable (Fairfield County, Connecticut)
New Haven Railroad Station (New Haven County, Connecticut)
New Jersey Hall (Middlesex County, New Jersey)
New London County Courthouse (New London County, Connecticut)
New Mexico Supreme Court Building (Santa Fe County, New Mexico)
New Portland Wire Bridge (Somerset County, Maine)
Suspension bridge over Carrabasset River on Wire Bridge Road in New Portland
New Scotland Avenue (Troop B) Armory (Albany County, New York)
New Smyrna Sugar Mill Ruins (Volusia County, Florida)
New Ulm Armory (Brown County, Minnesota)
New York Executive Mansion (Albany County, New York)
New York State Armory (Dutchess County, New York)
New York State Capitol (Albany County, New York)
New York State Inebriate Asylum (Broome County, New York)
Newark Broad Street Station (Essex County, New Jersey)
Newberry Hall (Washtenaw County, Michigan)
Newell Hall (Alachua County, Florida)
Newport Bridge (Jackson County, Arkansas)
Cantilevered through truss bridge on AR 367 (formerly US 67) over White River at Newport
Newsom's Mill (Davidson County, Tennessee)
Newtown Battlefield (Chemung County, New York)
Newtown Creek Bridge (Bucks County, Pennsylvania)
Niagara Falls Armory (Niagara County, New York)
Niagara Reservation (Niagara County, New York)
Nicholas Marnach House (Winona County, Minnesota)
Ninth District Lighthouse Depot (Berrien County, Michigan)
Niobrara River Bridge (Knox County, Nebraska)
Nocoroco (Volusia County, Florida)
NOQUEBAY (Schooner--Barge) Shipwreck Site (Ashland County, Wisconsin)
Norlin Quadrangle Historic District (Boulder County, Colorado)
North Carolina Central University (Durham County, North Carolina)
North Carolina Executive Mansion (Wake County, North Carolina)
North Carolina State Capitol (Wake County, North Carolina)
North Dakota Mill and Elevator (Grand Forks County, North Dakota)
North Dakota School of Forestry Main Old (Bottineau County, North Dakota)
North Dakota State University District (Cass County, North Dakota)
North Fork Bridge (Baxter County, Arkansas)
Four-span deck truss bridge over North Fork White River on AR 5 at Norfork
North Fork Payette River Bridge (Valley County, Idaho)
North Fork Saline River Bridge (Saline County, Arkansas)
North Gate Hall (Alameda County, California)
North Hall, University of Wisconsin (Dane County, Wisconsin)
UW's first building, now also part of the Bascom Hill Historic District
North Hamma Hamma River Bridge (Mason County, Washington)
North St. Vrain Creek Bridge (Boulder County, Colorado)
Northampton State Hospital (Hampshire County, Massachusetts)
Northern Michigan Asylum (Grand Traverse County, Michigan)
Northwest Company Post (Pine County, Minnesota)
Norwalk River Railroad Bridge (Fairfield County, Connecticut)
Norwich Hospital District (New London County, Connecticut)
Noyes Hall, State School for the Deaf (Rice County, Minnesota)
NYS Armory (Essex County, New York)
O'Donel House and Farm (Perry County, Pennsylvania)
O'Fallons Bluff (Lincoln County, Nebraska)
O.J. WALKER (shipwreck) (Chittenden County, Vermont)
Oahe Chapel (Hughes County, South Dakota)
Oak Hill (Cumberland County, Virginia)
Oak Lodge (Middlesex County, Connecticut)
Oakland Chapel (Claiborne County, Mississippi)
Oaklands, The (Kalamazoo County, Michigan)
Oakley Plantation House (West Feliciana Parish, Louisiana)
Ocean City 34th Street Station (Cape May County, New Jersey)
Ocean City Tenth Street Station (Cape May County, New Jersey)
Ocean Parkway (Kings County, New York)
OCEAN WAVE (Shipwreck) (Door County, Wisconsin)
Oconee State Park Historic District (Oconee County, South Carolina)
Oconee Station and Richards House (Oconee County, South Carolina)
Historic frontier outpost
Oconto Site (Oconto County, Wisconsin)
Octagon House (Fond du Lac County, Wisconsin)
Octagon House that was once a stop on the Underground Railroad.
Octagonal Schoolhouse (Kent County, Delaware)
Ogdensburg Armory (St. Lawrence County, New York)
Oglebay Hall (Monongalia County, West Virginia)
Ohio and Erie Canal (Cuyahoga County, Ohio)
A four mile section of the canal that connects the Ohio River & Lake Erie.
Ohio and Erie Canal Deep Lock (Summit County, Ohio)
Same as Lock # 28
Ohio Asylum for the Blind (Franklin County, Ohio)
Ohio Company Land Office (Washington County, Ohio)
Ohio Stadium (Franklin County, Ohio)
Ohio State Arsenal (Franklin County, Ohio)
Ohio State Normal College At Kent (Portage County, Ohio)
Ohio State Office Building (Franklin County, Ohio)
Ohio State Reformatory (Richland County, Ohio)
Ohio State Route 51 Bridge Over the Portage River (Ottawa County, Ohio)
Closed-spandrel arch bridge over Portage River on OH 51 in Elmore
Ohio Statehouse (Franklin County, Ohio)
Oil City Armory (Venango County, Pennsylvania)
Oklahoma City Discovery Well (Oklahoma County, Oklahoma)
Oklahoma Historical Society Building (Oklahoma County, Oklahoma)
Oklahoma State Capitol (Oklahoma County, Oklahoma)
Olana (Columbia County, New York)
Old Adobe Patio (Pima County, Arizona)
Old Armory --Vermillion (Clay County, South Dakota)
Old Bakery (Travis County, Texas)
Old Barracks (Mercer County, New Jersey)
Old Brown's Mill School (Franklin County, Pennsylvania)
Old Cahokia Courthouse (St. Clair County, Illinois)
Old Campus District, University of South Carolina (Richland County, South Carolina)
Old Capitol (Johnson County, Iowa)
Old Capitol Building (Thurston County, Washington)
Old Central University (Madison County, Kentucky)
Old City Road Stone Arch Bridge (Herkimer County, New York)
Stone arch bridge over City Brook on Old City Road
Old College Historic District (New Castle County, Delaware)
Old Columbia--Wrightsville Bridge (Unspecified county, Pennsylvania)
Open-spandrel arch bridge over Susquehanna River on PA 462 (Old Lincoln Highway) between Columbia and York Counties