Production is set to begin by 2010 and employment is projected at 2,000. The company said it expects to build 150,000 vehicles a year.
The plant will be built on a 1,700 acre site at Blue Springs, land that has been promoted for economic development.
Mississippi was chosen in a competition with Tennessee and Arkansas.
The plant will be the second automaker to locate in the state. Nissan Motor Corp. opened its assembly plant north of Jackson in 2003. The 4,000-employee plant produced about 278,000 vehicles last year.
Gov. Haley Barbour and two Toyota manufacturing executive vice presidents, Gary Convis and Ray Tanguay, announced the project in an auditorium at Tupelo High School.
"Toyota is the world's premiere auto manufacturer and our state will be the best partner the company has," Barbour said in prepared remarks.
Tanguay said several factors led to the decision to build in Mississippi over the other proposed sites.
"On my visit to northern Mississippi, I have talked with area companies and observed their work force," Tanguay said in prepared remarks. "What I observed were people who are educated, ethical and friendly with a strong work ethic - a perfect match for the Toyota way."
Lawmakers told The Associated Press that Barbour will call a special legislative session for Friday to address an incentive plan for Toyota.
The site is about 10 miles northwest of Tupelo.
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