Alexander Thom (October 26, 1775 – September 26, 1845) was a military surgeon, judge and political figure in Upper Canada.
He was born in Scotland in 1775, the son of a farmer named Alexander Thom, and studied at King's College in Aberdeen.
He was chosen as the surgeon for the military settlement at Perth in Upper Canada in 1815 and served as the doctor there until 1822.
Thom built a sawmill and gristmill on the Tay River at Perth.
Another daughter of his, Catherine Rosamund, married Chief Justice John Godfrey Spragge.