Working at a pace to buy or build nearly 60 stores each year, Casey’s General Stores Inc. now plans a major expansion that will nearly double the size of the company’s Ankeny headquarters to support that growth.

The company has filed a site plan with the city to add nearly 100,000 square feet of warehouse space and more than 19,000 square feet of office space to its office-warehouse complex located at One Convenience Blvd., just north of the Ankeny Regional Airport. As of March 1, Casey’s owned and operated 1,345 convenience stores in nine Midwestern states, with franchisees owning another 25.

Bill Walljasper, Casey’s chief financial officer, declined to comment on the proposed expansion, saying through his assistant that there was “nothing yet to report.”

According to documents filed with the city of Ankeny, the warehouse expansion will be built on the south end of the existing 146,128-square-foot building, which was originally built in 1989. The additional office space will be built onto the east side of the building, which faces Interstate 35. More parking for the company’s fleet of semitrailer trucks is planned along a triangular piece of land bordering the airport that the company purchased several years ago from the Polk County Aviation Authority.

Mike Pogge, a planner with the city’s community development department, estimated it will take two months to complete rezoning of the former airport land, after which the site plan will be sent to the Ankeny Plan and Zoning commission for consideration.

According to Casey’s third-quarter earnings report released last month, its annual goal is to acquire at least 43 stores and build 15 stores to achieve 3.5 percent total store growth. Through the first nine months of its fiscal year, which ends April 30, the company had purchased 22 stores, and had agreements pending for 20 more. The company has also built six stores and plans to open seven more by the end of this month.

During its previous fourth fiscal quarter, the company announced a decision to sell 36 underperforming stores, which Casey’s Chairman Ron Lamb called “the result of a strategic evaluation to position the company for future improved performance.” That move decreased third quarter-earnings to $2.46 million, or 5 cents per share, compared with $5.84 million, or 12 cents per share, a year ago. Without a one-time $7 million charge related to the sale of the stores, earnings per share would have been 14 cents, the company reported.