Mount Vernon, a 625-ton (burden) wooden screw steamship, was built at Brooklyn, New York in 1859. She was chartered by the U.S. Navy soon after the beginning of the Civil War and purchased in September 1861. In May 1861, while under charter, Mount Vernon went to the Gulf of Mexico. She captured one sailing vessel in that area and, in early July, was sent to Hampton Roads, Virginia, to join the blockade of the Confederacy's eastern coast. For much of the rest of the year, Mount Vernon operated in the Chesapeake Bay and adjacent rivers, making one more capture.

From November 1861 through the end of the Civil War, Mount Vernon primarily served off North Carolina. She was involved in the capture or destruction of eight would-be blockade runners, all sailing vessels, in 1862 and four more in 1863. In early May 1864, Mount Vernon engaged the Confederate ironclad Raleigh, which had come out to attack Federal warships blockading Wilmington. The following July, she made an unproductive search for the raider CSS Florida and, in mid-December, assisted in the destruction of another schooner. With the end of the Civil War in the spring of 1865, Mount Vernon was no longer needed by the Navy. She was decommissioned in June of that year and sold the next month. Mount Vernon then returned to commercial employment, keeping the same name, and was sold to foreign owners in 1869.