South Ann Street–Mill Street Historic District is a national historic district located at Little Falls in Herkimer County, New York. The district includes 15 contributing buildings and one contributing structure. They relate to the history of transportation and commercial/industrial development of the city. They include multi-story brick and stone commercial buildings, the former New York Central Railroad passenger station, remains of Erie Canal trunk and aqueduct, and a former hydroelectric power station and remains of the related dam.