In a deal valued at approximately $1.1 billion, Walgreen Co. has agreed to buy New York City drugstore chain Duane Reade from the private equity firm Oak Hill Capital Partners. Walgreen will pay $620 million in cash and assume $457 million in debt.

With 7,162 stores nationwide, Walgreen is the nation’s largest drugstore company. But it has only 70 stores in the New York City metropolitan area, including 15 in Manhattan. The acquisition is the largest ever for the Deerfield, Ill.-based company, which plans to retain the Duane Reade name and its executive management. The chain, which was started over a century ago as a single neighborhood pharmacy in Illinois by Charles R. Walgreen Sr., last year reported $63 billion in sales.