Orton Irwin Grain (August 9, 1863[1] – February 2, 1930[2]) was a Canadian physician and politician in Manitoba.

[3] Grain was one of the charter holders of the Winnipeg and Northern Railway, and served as mayor of Selkirk in 1896.

He supported the Conservative administration of Hugh John Macdonald and Rodmond Roblin, and sat as a government backbencher in the legislature which followed.

Grain defeated O'Donahue by 41 votes in the 1907 election, and again served as a backbench supporter of Roblin's government.

Grain made a number of suggestions for treating tuberculosis on reserves, but these were rejected for economic reasons.