- Older Worker Job Bank
- Oldham, H.R.
- Olfene, Fred
- Olfene, Henry
- Olfene, Henry L.
- Olfene, Mary
- Olfene, Richard
- Olheim, Helen
- Olin Arts Center
- Olive, Georgiana
- Oliver, Charles
- Oliver, Charles L.
- Oliver, Cyrus
- Oliver, John
- Oliver, Mary D.
- Olivier, Fr.
- Olivier, Herman
- Olivier, Joseph, fils
- Olsen, Pedar
- Olson, Lynn
- Olstein, Joel
- One Price Clothier
- Opera Houses and Music Halls of Maine
- Opium
- Orange Street
- Orcutt, Katie A.
- Ordway, A.K.
- Ordway, A.K., wife of
- Ordway, Albion
- Ordway, Lewis M.
- Ordway, Malcom
- Orestis Family
- Orestis, Antionette
- Orestis, George
- Orestis, John
- Orestis, Toni
- Organists
- Orlando, Griff
- Ornstein, Harry
- Orphanages
- Orpheon
- Orpheon Chorale Group
- Orr, Benjamin
- Orr, Charles
- Orr, Cordelia
- Orrs Island
- Osborn, Martha E.
- Osborne, -- (a son)
- Osborne, William
- Osgood & Son
- Osgood and Drew Jewelers
- Osgood Block
- Osgood House
- Osgood, --
- Osgood, -- (a son)
- Osgood, Aaron
- Osgood, Abbey T.
- Osgood, Albert
- Osgood, B.A., Esq
- Osgood, Brainard A.
- Osgood, C.H.
- Osgood, Charles
- Osgood, Charles H. (Col.)
- Osgood, Charles H. Mrs.
- Osgood, H. A. and Co.
- Osgood, H.A.
- Osgood, Henry
- Osgood, J.N. Mrs.
- Osgood, James
- Osgood, John F.
- Osgood, Nathaniel
- Osgood, S.B., Capt.
- Osgood, Sarah E.
- Osgood, Silas B.
- Osgood, Warren B.
- Osgoods Jewelry Store
- Osher, Thomas
- Ostroff, Max
- Oswald and Armstrong
- Oswell, Lena M.
- Otis & Cobb
- Otis, Etta S.
- Otis, Harrison G.
- Otis, J.H.
- Otis, John
- Otis, Lizzie
- Otis, Oliver
- Ouelette, Denise
- Ouellet, Cyprien
- Ouellet, Georges
- Ouellet, H.
- Ouellet, Henri C.
- Ouellette, Albert
- Ouellette, Alice
- Ouellette, Andre
- Ouellette, Arthur
- Ouellette, Bertrand
- Ouellette, Bertrand Mrs.
- Ouellette, Donna K.
- Ouellette, Emilio
- Ouellette, Fernand
- Ouellette, Florian
- Ouellette, Gertrude
- Ouellette, Guy
- Ouellette, Jane
- Ouellette, Laurette
- Ouellette, Leslie A.
- Ouellette, Lorraine
- Ouellette, Louis, veuve
- Ouellette, Maurice
- Ouellette, Mo
- Ouellette, Muguette
- Ouellette, Odile
- Ouellette, Pauline
- Ouellette, Philippe
- Ouellette, Reginald Mrs.
- Ouellette, Rejanne
- Ouellette, Richard G.
- Ouellette, Rita
- Ouellette, Roger
- Ouellette, Wilfred
- Oullette, Atter
- Our Lady of Lourdes Asylum
- Our Town Magazine
- Ovens, Norea
- Overseers of the Poor
- Owen & Little
- Owen and Hall
- Owen Cigar Co.
- Owen, Charles
- Owen, E.S.
- Owen, E.S., Mrs.
- Owen, Eli
- Owen, James
- Owen, Jennie H.
- Owen, John
- Owen, Mary
- Owen, Mr. (marble factory moved to Waldron's block)
- Owen, Officer
- Owen, R. M.
- Owen, Robert M.
- Owen, William
- Oxaard, E.J.
- Oxnard, W. A.