John Adams Dix (July 24, 1798 – April 21, 1879) was an American politician and military officer who was Secretary of the Treasury, Governor of New York and Union major general during the Civil War.

Dix was elected as a Democrat to the United States Senate to fill the vacancy caused by the resignation of Silas Wright, Jr., and held office from 1845 to 1849.

In February 1849, he ran for re-election to the U.S. Senate as the Barnburners' candidate, but the Whig majority of the State Legislature elected William H. Seward.

In addition to his military and public duties, Dix was the president of the Union Pacific from 1863 to 1868 during construction of the First transcontinental railroad.

At the outbreak of the Civil War, he sent a telegram to the Treasury agents in New Orleans ordering that: "If any one attempts to haul down the American flag, shoot him on the spot."

Although the telegram was intercepted by Confederates, and was never delivered to the Treasury agents, the text found its way to the press, and Dix became one of the first heroes of the North during the Civil War.

His importance at the beginning of the Civil War was in arresting six members of the Maryland General Assembly and thereby preventing the legislature from meeting.

(The cartel worked well for a few months, but broke down when Confederates insisted on treating black prisoners as fugitive slaves and returning them to their previous owners.)

Dix died on April 21, 1879, in New York City at age 80 and was buried at the Trinity Church Cemetery in Lower Manhattan.