Place of worship

Oak Plain Presbyterian Church (Sampson County, North Carolina)
Oakland Chapel (Claiborne County, Mississippi)
Oakland Grove Presbyterian Church (Alleghany County, Virginia)
Oakland Presbyterian Church (Fayette County, Tennessee)
Oakwood Cemetery Chapel (Allegan County, Michigan)
Oakwood Cemetery Chapel (Summit County, Ohio)
Oark School--Methodist Church (Johnson County, Arkansas)
Oblong Friends Meetinghouse (Dutchess County, New York)
Ocoee Christian Church (Orange County, Florida)
Oconaluftee Baptist Church (Swain County, North Carolina)
Ohave Shalom Synagogue (Sullivan County, New York)
Ohev Sholem Synagogue (New London County, Connecticut)
Ohev Sholom Temple (Cabell County, West Virginia)
Oil Springs Methodist Church (Johnson County, Kentucky)
Old Adobe Chapel of the Immaculate Conception (San Diego County, California)
Adobe house converted to a chapel Built in 1850 rebuilt by WPA in 1937
Old Bergen Church (Hudson County, New Jersey)
Old Bethany Church (Brooke County, West Virginia)
Old Bethel Methodist Church (Greene County, Arkansas)
Old Bethel United Methodist Church (Charleston County, South Carolina)
Old Blue River Friends Church (Washington County, Indiana)
Quaker Church built in 1815
Old Bluff Presbyterian Church (Cumberland County, North Carolina)
Old Bnai Zion Synagogue (El Paso County, Texas)
Old Brick Church (Windham County, Vermont)
Old Brick Church (Surry County, Virginia)
Old Brick Presbyterian Church (Colbert County, Alabama)
Old Broadway Synagogue (New York County, New York)
Old Cambridge Baptist Church (Middlesex County, Massachusetts)
Old Cathedral Complex (Knox County, Indiana)
The Greek Revival "Old Cathedral" is the key building in the district
Old Catholic Church (Yankton County, South Dakota)
Old Cedar Baptist Church (Owen County, Kentucky)
Old Chapel (Clarke County, Virginia)
Old Chapel Hall (Dubuque County, Iowa)
Old Christ Church (Windsor County, Vermont)
Old Christ Church (Sussex County, Delaware)
Old Christ Church (Escambia County, Florida)
Old Congregational Church (Providence County, Rhode Island)
Old Cumberland Presbyterian Church (Whitfield County, Georgia)
Old Danish Church (Bureau County, Illinois)
Old Donation Church (Virginia Beach, Virginia)
Old Drawyers Church (New Castle County, Delaware)
Old East Paint Creek Lutheran Church (Allamakee County, Iowa)
Old Ebenezer Church (Marion County, South Carolina)
Old Finnish Lutheran Church (Lawrence County, South Dakota)
Old First Church (Erie County, Ohio)
Old First Presbyterian Church (Essex County, New Jersey)
Old First Presbyterian Church (New Castle County, Delaware)
Old First Presbyterian Church (Suffolk County, New York)
Old First Presbyterian Church of Wilmington (New Castle County, Delaware)
Old First Reformed Church (Kings County, New York)
Old Fort Church (New Castle County, Delaware)
Old German Baptist Brethern Church (Forsyth County, North Carolina)
Old Hickory Methodist Church (Davidson County, Tennessee)
Old Holy Redeemer Catholic Church (Osceola County, Florida)
Old Holy Trinity Parsih (Floyd County, Indiana)
First Catholic Parish in New Albany Indiana
Old Jones Gap Church (Henderson County, North Carolina)
Old Judy Church (Pendleton County, West Virginia)
Old Kennett Meetinghouse (Chester County, Pennsylvania)
Old Kingsport Presbyterian Church (Sullivan County, Tennessee)
Old Log Church (Warren County, Kentucky)
Old Log Church (Bedford County, Pennsylvania)
German Reformed and Lutheran log church outside of Schellsburg, PA
Old Mulkey Meetinghouse (Monroe County, Kentucky)
Old Narragansett Church (Washington County, Rhode Island)
Old Newburgh Presbyterian Church (Warrick County, Indiana)
Old Norriton Presbyterian Church (Montgomery County, Pennsylvania)
Old North Church (Suffolk County, Massachusetts)
Old Ohavi Zedex Synagogue (Chittenden County, Vermont)
Old Peace Lutheran Church (Franklin County, Ohio)
Old Philadelphia Presbyterian Church (Gadsden County, Florida)
Old Pickens Presbyterian Church (Oconee County, South Carolina)
Historic church in Oconee County, SC
Old Pine Church (Hampshire County, West Virginia)
Historic church outside Purgitsville, WV
Old Plover Methodist Church (Portage County, Wisconsin)
Old Presbyterian Church (La Paz County, Arizona)
Old Presbyterian Church (Barnwell County, South Carolina)
Historic antebellum church in Barnwell, SC
Old Presbyterian Meeting House (Alexandria, Virginia)
Old Presbyterian Meeting House and Museum (Lincoln County, Kentucky)
Site of the first church built in Kentucky
Old Probst Church (Pendleton County, West Virginia)
Old Providence Presybterian Church (Halifax County, Virginia)
Old Providence Stone Church (Augusta County, Virginia)
Old Quaker Meetinghouse (Queens County, New York)
Old Roman Catholic Cathedral (Baltimore, Maryland)
Old Runnymede Church (Harper County, Kansas)
Old Saint Mary's Cathedral (San Francisco County, California)
Gothic Revival Church built 1854
Old Salem Church and Cemetery (Baltimore County, Maryland)
Old Santa Rosa Catholic Church and Cemetery (San Luis Obispo County, California)
Old School Baptist Church and Cemetery (Middlesex County, New Jersey)
Old School Baptist Church of Halcottsville (Delaware County, New York)
Old Scotch Church (Washington County, Oregon)
Old Ship Meetinghouse (Plymouth County, Massachusetts)
Old South Church (Lake County, Ohio)
Old South Church in Boston (Suffolk County, Massachusetts)
Old South Meetinghouse (Suffolk County, Massachusetts)
Old South Union Church (Norfolk County, Massachusetts)
Old Southeast Church (Putnam County, New York)
Old St. Anne's Church (New Castle County, Delaware)
Old St. Anthony's Catholic Church (Nueces County, Texas)
Old St. John's Church (Lorain County, Ohio)
Old St. Luke's Episcopal Church (Bell County, Texas)
Old St. Mary's Church (Milwaukee County, Wisconsin)
Oldest extant church in Milwaukee
Old St. Patrick's Cathedral Complex (New York County, New York)
Old St. Patrick's Church (Morgan County, Missouri)
Old St. Patrick's Church (Lorain County, Ohio)
Old St. Paul's Methodist Episcopal Church (New Castle County, Delaware)
Old St. Peter's Church (Westchester County, New York)
Old St. Teresa's Catholic Church (Dougherty County, Georgia)
Old St. Vincent's Church (Cape Girardeau County, Missouri)
Old Stone Church (Frederick County, Virginia)
Old Stone Church (Greenbrier County, West Virginia)
Old Stone Church (Worcester County, Massachusetts)
Old Stone Church (Cuyahoga County, Ohio)
Old Stone Church (St. Louis County, Missouri)
Old Stone Church (Cumberland County, New Jersey)
Old Stone Church (Winchester, Virginia)
Old Stone Church (Cass County, North Dakota)
Old Stone Church and Cemetery (Pickens County, South Carolina)
Historic meeting house style church in Pickens County, SC
Old Stone Presbyterian Church (Hunterdon County, New Jersey)
Old Synagogue (Dane County, Wisconsin)
Old Town Friends' Meetinghouse (Baltimore, Maryland)
Old Union Baptist Church (Madison County, Georgia)
Old Union Church and Cemetery (Daviess County, Indiana)
Old Union Meetinghouse (Franklin County, Maine)
Old Union Methodist Church (New Castle County, Delaware)
Old Waxhaw Presbyterian Church (Lancaster County, South Carolina)
Old Welcome Baptist Church (Anderson County, South Carolina)
Church north of Anderson, SC
Old West Church (Suffolk County, Massachusetts)
Old West Church (Washington County, Vermont)
Old Wye Church (Talbot County, Maryland)
Old Zion Methodist Church (Barren County, Kentucky)
Oldham Methodist Church (Kingsbury County, South Dakota)
Olive Branch Methodist Episcopal Church (Shelby County, Kentucky)
Olive Branch Missionary Baptist Church (Bedford County, Virginia)
Olivet Presbyterian Church (New Kent County, Virginia)
Olivet Presbyterian Church (York County, South Carolina)
Historic church in McConnells, SC
Omar Chapel (Seneca County, Ohio)
Omer Christian Church and Cemetery (Barrow County, Georgia)
Oneida Lake Congregational Church (Madison County, New York)
Only Baptist Church, Only, TN (Hickman County, Tennessee)
Only Baptist Church - at least they think it is
Opequon Presbyterian Church (Frederick County, Virginia)
Oquossoc Log Church (Franklin County, Maine)
Oran Community Church (Onondaga County, New York)
Orange Street Presbyterian Church (Garland County, Arkansas)
Orient Baptist Church (Ocean County, New Jersey)
Original Church of God (Giles County, Tennessee)
Original Congregational Church of Wrentham (Norfolk County, Massachusetts)
Oroville Chinese Temple (Butte County, California)
Orthodox Meetinghouse (Chester County, Pennsylvania)
Osterville Baptist Church (Barnstable County, Massachusetts)
Otsdawa Baptist Church (Otsego County, New York)
Ott's Chapel (New Castle County, Delaware)
Otter Lake Community Church (Oneida County, New York)
Otterbein Church (Baltimore, Maryland)
Otterbein Church (Jackson County, West Virginia)
Our Lady Help of Christians Catholic Church (Ste. Genevieve County, Missouri)
Our Lady of Good Voyage Church (Essex County, Massachusetts)
Our Lady of Grace Church (St. John the Baptist Parish, Louisiana)
Our Lady of Guadaloupe Church (Coconino County, Arizona)
Our Lady of Guadalupe Mission Chapel (1953-1960) (Santa Clara County, California)
Our Lady of Lourdes Cathedral (Spokane County, Washington)
Italian Romanesque Revival cathedral built between 1903 and 1908
Our Lady of Lourdes Church (Victoria County, Texas)
Our Lady of Lourdes Church Complex (Providence County, Rhode Island)
Our Lady of Mercy Chapel (Morris County, New Jersey)
Our Lady of Mount Carmel Church (Mahoning County, Ohio)
Our Lady of Mt. Carmel Church (Bernalillo County, New Mexico)
Our Lady of Peace Cathedral (Honolulu County, Hawaii)
Our Lady of Perpetual Help Church (Franklin County, Arkansas)
Our Lady of Purication Catholic Church (Dona Ana County, New Mexico)
Our Lady of Sorrows Chapel (La Crosse County, Wisconsin)
Our Lady of Sorrows Church (San Miguel County, New Mexico)
Our Lady of Sorrows Church (Sandoval County, New Mexico)
Our Lady of the Rosary Catholic Church (San Diego County, California)
Romanesque Revival Catholic church built in 1923
Our Lady of Victory Catholic Church (Cochise County, Arizona)
Our Lady Queen of Peace Church (Lincoln County, Maine)
Our Lady Sorrows Catholic Church (Sweetwater County, Wyoming)
Our Lady, Queen of Heaven Church (Owyhee County, Idaho)
Our Mother of Sorrows Monastery and Retreat Center (Hampshire County, Massachusetts)
Our Savior's Lutheran Church (Yankton County, South Dakota)
Our Savior's Lutheran Church (Humboldt County, California)
Carpenter Gothic Lutheran church built in 1899
Our Savior's Scandinavian Lutheran Church (Ward County, North Dakota)
Our Saviour's Evangelical Lutheran Church (Manistee County, Michigan)