Decatur sailed from Hampton Roads, Virginia 1 March 1847, and after a brief stay at the Pensacola Navy Yard, arrived off Castle Juan de Uloa, Mexico, 14 April, for duty in the Mexican–American War.

Rejoining the African Squadron, Decatur cruised on the northwest coast of Africa on the lookout for slave ships and protecting U.S. interests from 2 February 1848 to 15 November 1849.

After a period in ordinary she sailed from Portsmouth, New Hampshire, for duty with the Home Squadron, cruising off the Atlantic Coast and in the Caribbean until arriving at Boston 21 August 1852 where she was decommissioned for repairs.

Recommissioned 12 July 1853 Decatur joined a Special Squadron to guard the fishing interests of American citizens in North Atlantic Ocean waters, returning to Boston in September to prepare for distant service.

[1] After searching for the missing merchant ship San Francisco in the Caribbean in January and February 1854, she sailed from Norfolk 16 June to join the Pacific Squadron.

On 13 June 1856, she arrived at Mare Island Navy Yard for repairs, and on 8 January 1857, sailed for Panama, touching at Central American ports for the protection of U.S. interests.

She was decommissioned at Mare Island 20 June 1859 and remained in ordinary until March 1863 when she was fitted as a defensive floating battery and stationed off San Francisco.