The district is a 25.8-acre (10.4 ha) area shaped roughly like an upside down "Y".
Its boundaries mostly follow property lines and street curbs.
It is built around South Highland Avenue (U.S. Route 9), the main north–south through road, and Main Street, which leads west to the river.

At its northern end is 21–22 Croton Avenue, adjacent to the village municipal building along (New York State Route 133).
It includes the bank building at the corner with South Highland and then crosses the street to follow the rear line of all the properties on Main Street, the area traditionally known as the Crescent due to the curve resulting from the area's topography.
This takes it to the southwest, crossing the aqueduct trailway.
At Brandreth Street it veers westward to take in the properties to 55 Central Avenue and, to their south, 107 Main Street.

Then it returns eastward along Main, crossing the aqueduct again to the north side of Church Street.
It turns south to follow the rear lines of the properties along South Highland, two commercial buildings and Trinity Episcopal Church, then returns to South Highland at Maple Place.
It follows the east side of the road to Emwilton Place, where it turns east to include Ossining United Methodist Church.
Past the church it turns north again to include all the buildings of Ossining High School while excluding its more modern athletic facilities.
At the high school property's north boundary it turns west again to the rear lines of properties on South Highland, and follows them back to Village Hall.

The 37 buildings and structures within these boundaries are overwhelmingly commercial structures, usually brick buildings of two or three stories.
The rest are institutional, either religious or governmental in use.
All but 14 are considered contributing properties.

Within the district the land slopes slightly to the north and west, anticipating steeper drops of almost 100 feet (30 m) to the Sing Sing Kill gorge and Hudson.
As a result of its proximity to these bluffs the district has a view across the Hudson.
To the east and south are the residential neighborhoods of Ossining; in 2013 the district boundary was expanded to include Highland Cottage, also listed on the Register.

The village's 2009 comprehensive plan called for expanding the historic district boundaries, at least for local purposes.
Four small areas were proposed for inclusion: the additional properties on Central Avenue, a westward expansion along Main Street, Highland Cottage and the building to the east of the municipal building on Croton Avenue at the northeast corner of the district.
These areas were added to the district by the U.S. National Park Service in 2013.
The district is a 25.8-acre (10.4 ha) area shaped roughly like an upside down "Y". Its boundaries mostly follow property lines and street curbs. It is built around South Highland Avenue (U.S. Route 9), the main north–south through road, and Main Street, which leads west to the river.
At its northern end is 21–22 Croton Avenue, adjacent to the village municipal building along (New York State Route 133). It includes the bank building at the corner with South Highland and then crosses the street to follow the rear line of all the properties on Main Street, the area traditionally known as the Crescent due to the curve resulting from the area's topography. This takes it to the southwest, crossing the aqueduct trailway. At Brandreth Street it veers westward to take in the properties to 55 Central Avenue and, to their south, 107 Main Street.
Then it returns eastward along Main, crossing the aqueduct again to the north side of Church Street. It turns south to follow the rear lines of the properties along South Highland, two commercial buildings and Trinity Episcopal Church, then returns to South Highland at Maple Place. It follows the east side of the road to Emwilton Place, where it turns east to include Ossining United Methodist Church. Past the church it turns north again to include all the buildings of Ossining High School while excluding its more modern athletic facilities. At the high school property's north boundary it turns west again to the rear lines of properties on South Highland, and follows them back to Village Hall.
The 37 buildings and structures within these boundaries are overwhelmingly commercial structures, usually brick buildings of two or three stories. The rest are institutional, either religious or governmental in use. All but 14 are considered contributing properties.
Within the district the land slopes slightly to the north and west, anticipating steeper drops of almost 100 feet (30 m) to the Sing Sing Kill gorge and Hudson. As a result of its proximity to these bluffs the district has a view across the Hudson. To the east and south are the residential neighborhoods of Ossining; in 2013 the district boundary was expanded to include Highland Cottage, also listed on the Register.
The village's 2009 comprehensive plan called for expanding the historic district boundaries, at least for local purposes. Four small areas were proposed for inclusion: the additional properties on Central Avenue, a westward expansion along Main Street, Highland Cottage and the building to the east of the municipal building on Croton Avenue at the northeast corner of the district. These areas were added to the district by the U.S. National Park Service in 2013.
Downtown Ossining Historic District