County seats are displayed in UPPER CASE. Note: Information about zip codes, territorials, markings, etc. have been moved to detail pages for places that have links.
Post Office County Dates of Service
O’Day
Barry
1886-1891
O’Fallon
Saint Charles
1859-Present
O’Neill
Saint Louis
1888-1891, 1900-1901
Oak
De Kalb
1894-1906
Oak City
Grundy
1871-1872
Oak Dale
Shelby
1878-1905
Oak Grove
Jackson
1840-1862, 1867-Present
Oak Hill
Crawford
1870-1944
Oak Mound
Ozark
1888-1932
Oak Point
Randolph
1831-1838
Oak Point
Moniteau
1856-1865
Oak Ridge
Cape Girardeau
1854-1862, 1865-Present
Oakdale
Marion
1834-UNK
Oakdale
Shelby
?-1862
Oakfield
Franklin
1847-1895
Oakhill
Gasconade
1857-1870
Oakhurst
Miller
1862-1871
Oakland
Pulaski
1841-1849
Oakland
Laclede
1849-1863, 1865-1955
Oakley
Lewis
1851-1855
Oakley
Macon
1884-1888
Oakside
Shannon
1890-1943
Oakton
Barton
1897-1901
Oakville
Saint Louis
1841-1852, 1876-1907
Oakwood
Saint Charles
1858-1865
Oakwood
Marion
1887-1953
Oasis
Taney
1906-1951
Oates
Reynolds
1887-1920
Oberlin
Nodaway
1888
Oby
Crawford
1910-1921
Oceola
Jefferson
1837-1838
Ocie
Ozark
1908-1967
Octa
Dunklin
1903-1908
Odale
Barton
1881-1884
Odam
Putnam
1882
Odd
Texas
1884, 1892-1898
Odessa
Lafayette
1879-Present
Odin
Wright
1882-1915
Oermann
Jefferson
1888-1955
Ogden
Scott
1836-1840
Ogden
New Madrid
1839-1870, 1884-1893
Ogles Mills
Andrew
1858-1861
Ohio
Andrew
1851-1852
Ohio
Saint Clair
1878-1941
Ohio City
Mississippi
1846-1849
Ohio Mills
Andrew
1856-1860
Ohlman
Reynolds
1907-1915
Oil Spring
Osage
1866-1867
Ojibway
Wayne
1901-1907, 1924-1940
Okete
Lincoln
1887-1907
Oland
Harrison
1897-1902
Olathe
Douglas
1895-1908
Old Alexandria
Lincoln
1852-1880
Old Appleton
Cape Girardeau
1917-Present
Old Buck Station
Jefferson
1858
Old Dutch
Jefferson
1872-1882
Old Franklin
Howard
1830, 1851-1854, 1888-1903
Old Jefferson
Saline
1838-1845
Old Mills
Washington
1867-1868
Old Mines
Washington
1827-1861, 1863-1969
Old Monroe
Lincoln
1863-Present
Old Orchard
Saint Louis
1886-1901
Olden
Howell
1883-1951
Oldfield
Christian
1900-Present
Olean
Miller
1885-Present
Olga
Webster
1890-1901
Olga
Christian
1901-1906
Olga
Douglas
1912-1918
Olinger
Lawrence
1902-1917
Olio
Macon
1860-1868
Olive
Dallas
1884-1907
Olive Branch
Holt
1850-1853, 1855-1859
Olive Hill
Johnson
1910-1912
Olivers Prairie
Newton
1841-1858
Olivette
Saint Louis
1908-1917
Olney
Lincoln
1876-Present
Olympia
Cedar
1899-1907
Omaha
Putnam
1860-1908
Omba
Douglas
1892-1920
Omega
Wright
1888-1892, 1895-1905
Omega
Laclede
1894
Omelet
Audrain
1854-1855
Omer
Cedar
1889-1907
Omo
Douglas
1899-1904
Oneida
Harrison
1884-1886
Ongo
Douglas
1897-1949
Onie
Dent
1895-1897
Only
Stone
1899-1900
Only
Camden
1907-1919
Ono
Grundy
1876-1881
Onyx
Pulaski
1836-1841
Onyx
Washington
1892-1895
Opel
Sullivan
1882-1902
Oran
Scott
1882-Present
Orange
Benton
1846-1851, 1854-1856, 1879-1880
Orange
Lawrence
1894-1903
Orchard Farm
Saint Charles
1894-1953
Orchard Grove
Mc Donald
1878
Orchard Point
Shannon
1876-1878
Orchard Switch
Carter
1890-1891
Orchid
De Kalb
1880-1900
Ore
Cass
1882-1906
Orearville
Saline
1875-1903
OREGON
Holt
1843-Present
Orel
Sullivan
1891-1894
Origanna
Laclede
1901-1920
Oriole
Cape Girardeau
1879-1905
Orion
Daviess
1856-1858
Orion
Henry
1870-1871
Orion
Saint Clair
1871
Orla
Laclede
1880-1954
Orleans
Polk
1846-1895
Orlinda
Linn
1879-1885, 1888-1898, 1900-1902
Oronogo
Jasper
1874-Present
Orr
Webster
1858-1863
Orrick
Ray
1873-Present
Orrsburg
Nodaway
1881-1902
Orrville
Saint Louis
1868-1895
Orton
Ray
1899-1900
Osa
Barry
1895-1908
Osage
Crawford
1836-1886
Osage Beach
Camden
1935-Present
Osage Bend
Cole
1908-1921
Osage Bluff
Cole
1858-1864, 1866-1912
Osage City
Cole
1856-1962
Osage Ferry
Gasconade
1828-1832
Osage Fork
Laclede
1854-1861
Osage Iron Furnace
Camden
1872
Osage Iron Works
Camden
1872-1931
Osaka
Taney
1905-1917
Osborn
De Kalb
1858-Present
Oscar
Texas
1880-1915
OSCEOLA
Saint Clair
1842-Present
Oseola
Rives
1839-1842
Osgood
Sullivan
1888-1965
Oshawa
Osage
1867-1874
Osiris
Cedar
1901-1906
Osiris
Cedar
1901-1906
Oskaloosa
Barton
1894-1953
Osta
Ozark
1900-1902, 1907-1914
Osterville
Caldwell
1869-1874
Oswald
Atchison
1894-1901
Oswego
Douglas
1905-1922
Otis
Polk
1899-1901
Otley
Webster
1904-1906
Oto
Stone
1877-1913
Otsego
Ray
1851-1871
Otter Creek
Wayne
1853-1876, 1885-1888
Otterville
Cooper
1848-Present
Ottomer
Douglas
1879-1909
Oval
Harrison
1897-1903
Overland
Saint Louis
1910-1925
Overton
Cooper
1864-1944
Ovid
Cass
1857-1860
Ovid
Ray
1888-1904
Owasco
Sullivan
1858-1861, 1866-1919
Owen
Lincoln
1883-1915
Owenmont
Ripley
1911-1915
Owens Mills
Osage
1876-1887, 1889-1922
Owens Station
Saint Louis
1834-1843
Owensville
Clay
1839-1844
Owensville
Gasconade
1856-Present
Owington
Warren
1855
Owl Creek
Knox
1872-1877
Owlcreek
Saint Francois
1901-1905
Owls Bend
Shannon
1923-1955
Owsley
Johnson
1877-1906
Oxford
Gentry
1859-1861
Oxford
Worth
1861-1905
Oxly
Ripley
1900-Present
Oyer
Saint Clair
1882-1935
Oyster
Lewis
1856-1876
Ozark
Greene
1840-1861
OZARK
Christian
1861-Present
Ozark Beach
Taney
1919-1959
Ozark Iron Works
Phelps
1873-1882
Ozark Mills
Iron
1871-1887
Ozora
Ste. Genevieve
1900-1914
178 Post Offices entered in the letter “O”
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Updated on 27 Nov 2009 23:28:52.
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Missouri Postal History Society, St. Louis, Missouri.