[1] In the late 1880s McIlhenny worked as a clerk on a ship in the Gulf of Mexico, but returned to Avery Island on the death of his father in 1890.

[2] In 1898 McIlhenny resigned from the company to serve in the Spanish–American War, joining Theodore Roosevelt's Rough Riders volunteer cavalry regiment.

"[B]y his high qualities and zealous attention to duty," wrote Roosevelt in his memoir of the campaign, McIlhenny "speedily rose to a sergeantcy, and finally won his lieutenancy for gallantry in action.

He resigned in 1919, however, to accept a position with the U.S. State Department as a financial adviser to Haiti, during the island republic's occupation by the U.S. Marines.

[5] The writer and civil rights activist James Weldon Johnson was among his critics, writing that "Mr. McIlhenny's unfitness by training and experience for the delicate and important position which he is filling was one of the most generally admitted facts which I gathered in Haiti.