David Roeder is a spokesman for the Illinois Department of Commerce and Economic Opportunity.
He says Chicago-based Boeing narrowed 54 proposed locations for the multi-billion factory down to about five. He says that short list included Rockford.
Boeing spokesman Doug Alder told the Chicago Sun-Times he wouldn't say which sites were finalists.
States across the country were trying to win the assembly plant and its 8,500 jobs.
But Boeing agreed to build the new plane in Washington after a union narrowly approved an eight-year contract last week.
Boeing is still making supply chain decisions for the plane.