O’Bryan, Roger (c. 1763) and his wife Ellen came from Ireland to Upper Canada by 1797 and settled in Woodhouse Township. Includes children 

O’Carr, Peter (1794-1856) married Susannah Beemer about 1820 and settled in Townsend Township. Includes three generations of descendants 

Oakes, James (1766-1856) went with his parents from Massachusetts to New Brunswick, then came to Charlotteville Township in 1803. His brothers Benjamin Oakes (1769) and Christopher Oakes (1773-1847) arrived at Charlotteville Township in 1804 and by 1805 respectively. Includes three generations of descendants 

Olds, Archibald (1788-1858) came from Stillwater, New York to Woodhouse Township by 1820. Includes three generations of descendants. Cortland Olds (1798-1880) came from the United States to Woodhouse Township by 1812 and married Catharine Kniffen.  Includes three generations of descendants. 

Omstead, Gideon (c. 1760-1797) came from the United States to Townsend Township in 1793. Includes four generations of descendants. Stephen Olmstead (1787-1854) came from Canaan, Columbia County, New York to Norfolk in 1818. He married widow Mary (Barber) Gilbert and settled in Middleton Township. Includes children and grandchildren 

Osborn, David (1799-1878) came from Dutchess County, New York to Ontario before 1839 and settled in Erie View, Walsingham Township. Includes children and grandchildren 

Ostrander, John (1763-1851) and his wife Christiana Cohoe settled in Crowland Township, Welland County, Upper Canada then moved to Bayham Township, Elgin County, and finally lived in Middleton Township. Includes five generations of descendants. Andrew Ostrander (c. 1760-) settled at Niagara, Upper Canada by 1786 then in Townsend Township, Norfolk County in 1797. Isaac Ostrander (c. 1797-) and his wife Mary settled in Middleton Township by 1848. Includes three generations of descendants. Isaac Ostrander (c. 1798) and his wife Naomi settled in Middleton Township by 1842. Includes children and grandchildren

Outhouse, Nicholas (1726) lived at Haverstraw Township, Orange County, New York in colonial times. During the American Revolution he joined Colonel Robinson’s Corps of Loyalists and afterwards went in the exodus of New York to Nova Scotia. He returned to Haverstraw by 1790 and then came to Charlotteville Township in 1796. Includes ancestry, children and grandchildren 

Overbaugh, Hezekiah (1784-1846) and his wife Mary Martha Wolven came from Cobleskill, New York to Walsingham Township by 1812. Includes ancestry and three generations of descendants 

Overholt, Staats (c. 1798-1873) and his brother Henry Overholt (1810-1873) settled in Charlotteville Township. Includes ancestry, children and grandchildren. Isaac Overholt (c. 1812-1897) lived at Rainham Township, Haldimand County then in Townsend Township. Includes children and grandchildren

Owen, Epenetus (1741- c. 1807) served as a patriot soldier during the American Revolution and settled afterwards at Chemung, New York. He came to Upper Canada in 1795 and settled in Caistor Township, Lincoln County then in 1799 came to Charlotteville Township. Includes five generations of descendants