The subsidiary of Smithfield, Va.-based Smithfield Foods Inc. said the plant that employs more than 3 percent of the city's workers would close April 20.
John Morrell President Joseph B. Sebring cited the age of the plant, which was built in 1959, and the struggling economy in announcing the closure.
"The Sioux City plant is one of the oldest, most outdated and least efficient plants in the Smithfield system," Sebring said in the statement.
Sebring said although the company is constantly improving its facilities, the Sioux City plant would "require significant capital expenditures" to update.
"In this adverse business environment those capital needs simply cannot be met," he said.
The company said it will honor all production contracts at Sioux City and that Smithfield Foods has no further plans to close plants "in the foreseeable future."
Sioux City's labor force is made up of about 43,400 workers older than 16, according to U.S. Census Bureau figures, meaning the John Morrell closing represents a loss of 3.3 percent of the city's workers.
Sioux City officials learned of the closing Tuesday afternoon. Economic Development Director Marty Dougherty said in a statement that Mayor Mike Hobart was contacted by John Morrell plant manager Dan Pacquin.
Dougherty did not immediately return telephone messages from The Associated Press on Wednesday.
Gov. Chet Culver called the plant closing "heartbreaking."
"My administration has been in communication with Smithfield, and we were prepared and ready to work with them on ways to bring new investment into the plant. Unfortunately, as a result of this national economic recession, Smithfield executives made the decision to close this facility," Culver said in statement.
Culver said the state will work with Sioux City to attract new businesses and find new jobs for the employees.
Sebring said some of Sioux City's production would be moved to other Smithfield plants in Denison, Iowa; Sioux Falls, S.D.; and Crete, Neb. The move would not require the company to add employees, he said.
A telephone call to Smithfield Foods, the nation's largest pork producer, was not immediately returned Wednesday.
While unfortunate, the Sioux City plant closing is not unexpected, said Dave Warner, spokesman for the National Pork Producers Council.
"It's a casualty of a two-year plus economic crisis that pork industry has been in," he said.