Post Office Square (est. 1874) in Boston is a square located in the financial district at the intersection of Milk, Congress, Pearl, and Water Streets. It was named in 1874 after the United States Post Office and Sub-Treasury which fronted it, now replaced by the John W. McCormack Post Office and Courthouse.

The square is almost entirely occupied by a privately owned and managed but publicly accessible park, Norman B. Leventhal Park, named for the Boston building manager and designer who designed it. It sits above a parking garage that descends to 80 feet below the surface, at the time one of the deepest points of excavation in the city. Revenues from parking fund the maintenance of the park. The 1.7-acre park is a popular lunchtime destination for area workers. It features a café, fountains, and a pergola around a central lawn, and the management provides seat cushions for visitors during the summer.