Other new construction continued in previously established styles.
In 1911 and 1913 respectively, new brick commercial buildings went up at 189 and 205 Main in the Renaissance Revival style.
Their application differed from those that had gone before.
On 189 was a belt course and stone quoins; on the other building all the decoration, including the flat-arched lintels and corbeled cornice, was brick.

In 1914, the bank buildings were complemented by the village's own new municipal building.
The stone edifice at 16–20 Croton Avenue, the northern end of the district, was in the Classical Revival mode common for most governmental buildings of the era.
The upper floors were initially used as a school.
It is the only Westchester building by Donn Barber, designer of the Connecticut State Library and the first American admitted to the French Society of Beaux-Arts architects.

Later that year another new architectural style was introduced to the district.
The Spanish Colonial Revival commercial building at 201–203 Main Street used a tiled pent-roofed parapet and stucco face.
Down the street at 125 Main, a 1920 building is the district's only example of a yellow brick building with limestone trim, in the form of a stone cornice topped with a parapet.

The early 1920s brought changes to Ossinging as the village's population reached 12,000, many moving into former farms newly subdivided into suburban residential neighborhoods on the village's outskirts.
In 1920, a new warden at the prison shut down several prison industries, including the quarry.
 Two years later, the Olive Opera House closed after almost 60 years.
It was soon converted into a small factory.
Two years after that, in 1924, the trolley system was shut down and dismantled, as more residents owned cars and more of the roads were paved.
Bus service replaced it.

The last significant buildings in the future historic district came to South Highland at the end of the decade.
On the corner just south of the First Baptist Church, the Cynthard Building, a single-story commercial block faced in terra cotta topped by a polychrome parapet, was erected in 1930; the Romanesque Revival doctor's office that had replaced the Union Hotel in 1890, and a house to the south, were demolished.
Also that year, the third and last bank building downtown was built at 13 Croton Avenue, the corner with North Highland.
The First National Bank, which had occupied the spot since 1880, moved into the district's only Art Deco building.
It has an unusual neoclassical door surround.

Ossining High School was that year's most distinguished addition.
Washington School, the village's high school since 1907, was becoming inadequate for the growing student population.
After several attempts, voters in 1929 approved a new building when a nearby private school made a donation that helped cover the $750,000 ($9.1 million in 2019) construction cost.
The new high school was on the site of Careswell, formerly the estate of Henry Baker, the local financier who had helped fund the Methodist church.
James Gamble Rogers was the architect.
Known for his many buildings on college campuses, the village's high school was one of his few secondary school buildings, and the only public school.
The Collegiate Gothic building, taking up the large area of South Highland's west side between the houses and the Methodist church, has some similarities to Harkness Tower at Yale University, also designed by Rogers and considered one of the best examples of that style.
Other new construction continued in previously established styles. In 1911 and 1913 respectively, new brick commercial buildings went up at 189 and 205 Main in the Renaissance Revival style. Their application differed from those that had gone before. On 189 was a belt course and stone quoins; on the other building all the decoration, including the flat-arched lintels and corbeled cornice, was brick.
In 1914, the bank buildings were complemented by the village's own new municipal building. The stone edifice at 16–20 Croton Avenue, the northern end of the district, was in the Classical Revival mode common for most governmental buildings of the era. The upper floors were initially used as a school. It is the only Westchester building by Donn Barber, designer of the Connecticut State Library and the first American admitted to the French Society of Beaux-Arts architects.
Later that year another new architectural style was introduced to the district. The Spanish Colonial Revival commercial building at 201–203 Main Street used a tiled pent-roofed parapet and stucco face. Down the street at 125 Main, a 1920 building is the district's only example of a yellow brick building with limestone trim, in the form of a stone cornice topped with a parapet.
The early 1920s brought changes to Ossinging as the village's population reached 12,000, many moving into former farms newly subdivided into suburban residential neighborhoods on the village's outskirts. In 1920, a new warden at the prison shut down several prison industries, including the quarry.  Two years later, the Olive Opera House closed after almost 60 years. It was soon converted into a small factory. Two years after that, in 1924, the trolley system was shut down and dismantled, as more residents owned cars and more of the roads were paved. Bus service replaced it.
The last significant buildings in the future historic district came to South Highland at the end of the decade. On the corner just south of the First Baptist Church, the Cynthard Building, a single-story commercial block faced in terra cotta topped by a polychrome parapet, was erected in 1930; the Romanesque Revival doctor's office that had replaced the Union Hotel in 1890, and a house to the south, were demolished. Also that year, the third and last bank building downtown was built at 13 Croton Avenue, the corner with North Highland. The First National Bank, which had occupied the spot since 1880, moved into the district's only Art Deco building. It has an unusual neoclassical door surround.
Ossining High School was that year's most distinguished addition. Washington School, the village's high school since 1907, was becoming inadequate for the growing student population. After several attempts, voters in 1929 approved a new building when a nearby private school made a donation that helped cover the $750,000 ($9.1 million in 2019) construction cost. The new high school was on the site of Careswell, formerly the estate of Henry Baker, the local financier who had helped fund the Methodist church. James Gamble Rogers was the architect. Known for his many buildings on college campuses, the village's high school was one of his few secondary school buildings, and the only public school. The Collegiate Gothic building, taking up the large area of South Highland's west side between the houses and the Methodist church, has some similarities to Harkness Tower at Yale University, also designed by Rogers and considered one of the best examples of that style.
Downtown Ossining Historic District