Macomb was born in Ballynure, County Tyrone, and emigrated to North America in 1755, his father having already settled there some years before (a typical emigration pattern of that time). They at first settled in New York, then moved to Detroit, where Alexander Macomb, along with his brother William, amassed a considerable fortune in the fur trade. One of his business partners was John Jacob Astor. He eventually returned to New York City, where he began to speculate in land. He also had constructed a huge mansion on Broadway which was occupied for a time by George Washington.

The brothers were aided in their business by the arrival of Henry Hamilton, an ambitious Scottish-born officer who would become their strong supporter in his dual rôle as lieutenant governor and superintendent of Detroit. His responsibilities included that for regulating the fur trade and keeping the Naive Americans at peace. He took up his responsibilities on Nov. 9, 1775. During the War of Independence, the Macombs were able to make considerable amounts of money selling all kinds of items and goods especially to Native Americans, who were siding with the British, and it has long been suspected that Macomb was at least implicit in supplying for use scalping knives, which he in any case did in large quantities. His rôle here was described by one recent historian as subordinate but rather clearly reprehensible. Certainly, he carried on a lot of business in wartime trading in scarce merchandise and military supplies After the war he and some business collaborators returned to New York, perhaps a risky move for someone with his record of pro-British stance and actions; (though one source writes that rather "neutralist than loyalist in the Revolution, above all they were entrepreneurs, profit-hungry to the core, and more akin to patriot merchants than Tory ideologues: His brother William remained at Detroit.

His speculations in business were so extravagant that he either made millions, or owed millions.  In 1787 he purchased 6,240,000 acres in upstate New York, followed by further purchases of similar size in several other states. His most famous - or infamous - transaction came in 1791 in was what was known as "Macomb's purchase" and involved the purchase of 3,600,000 acres in New York State, and was controversial as it was generally agreed that he had paid a very low price for state land. There has been speculation that Macomb was engaging in questionable business practices, possibly including bribery but almost some kind of sharp practice. Some have however pointed up another side to him; contemporaries described him as public-spirited and generous, and he served twice in the New York state legislature, though there is little evidence that he was an active or enthusiastic member. He was though an active member of the Society of the Friendly Sons of Saint Patrick, which was primarily a social organisation (which did of course bring him potential business contacts) of which Macomb was a sometime office-bearer.

With "Macomb's purchase" he overreached himself, and during the financial crisis of 1792, which occurred partly as a result of his speculations, he was ruined; debtors were not able to pay their debts to him quickly enough for Macomb to pay his own, which totalled $300,000 and landed him in debtor's prison. He never recovered financially, dying bankrupt. One of his many sons (he had a total of 17 children from two marriages as well as household of 25 servants including 10 slaves, making him the third-biggest slaveholder in New York) was another Alexander Macomb, a soldier who won a famous victory at Plattsburgh in the 1812 war against the British, and who later became the most senior general in the United States Army.

Born:	1748
Died:	1832