Brookside was listed on the National Register of Historic Places in 1975. Portions of the content on this web page were adapted from a copy of the original nomination document. 
Brookside (also known as Aldridge House; 6 Charlton Street) is located in Balston Spa on the flats at the base of Mohican Hill. The heavy growth of woods behind it and the rambling creek in front of the structure emphasize the rural setting.
It is obvious at first glance that the Brookside building was constructed in stages, resulting in a structure five bays wide by nine bays long. The front block consists of a five by three bay, two and a half story structure with roof ridge paralleling the street. Later partitioning on the interior conceals the fact that this block probably had the central hall, one room deep type of plan commonly found in Georgian influenced structures.
A later porch with full height square pillars runs across Brookside's facade. At the rear, are a long two and a half story extension half the width of the front block, and an adjacent small two story shed roofed section.
History records that this rear extension was preceded by a kitchen. Another addition, a ballroom on the north side of the house, was moved across the street to become a residence.
The foundation of the front block is fieldstone. The block is sheathed with both beaded and plain clapboards. The steeply pitched gable roof is covered with asphalt shingles. There are three dormer windows. Sash are double hung; the number of lights varies. Inside end chimneys and a heavy panelled entrance door with sidelights contribute to the portrait of a rural federal period structure derived from Georgian architecture.
The framing of this front section is hand hewn. The ceilings are low. Numerous changes to the interior of Brookside have left a residue of early and mid-19th century woodwork. The stairway is embellished by simple brackets applied to the string. The railing has slender balusters, turned newels and appears to date from c.1860.
There is little or no original hardware. A full cellar extends under this part of the house and also under the small rear addition. Evidence indicates that the Greek Revival design porch replaced an earlier similar porch.
The ridge of the gable roof of the large rear extension is perpendicular to that of the front block. Foundation and wall materials are similar to those of the front block. A cellar extends underneath the front portion of this part of the structure, a crawl space under the remainder. The character of this rear extension is strictly utilitarian.
Brookside was constructed in the wilderness to serve the needs of visitors to the first mineral spring to be used by the white man. Brookside continued to play a role in the history of Ballston Spa throughout subsequent uses as private school, military academy, home and apartment house. Presently owned by the Saratoga County Historical Society, whose goal is its preservation, Brookside is one of those buildings whose successive alterations have created a harmonious whole and a record of changing times in the community.
Meanwhile, new hotels were being built and new wells drilled to service them. Probably as a result of these activities the old spring failed in 1835. Eventually in 1847, a new spring was drilled. Called the Old Iron Spring, it is located just north of Brookside.
During the early and mid-19th century, resorts were also being developed in other areas which had mineral springs. Saratoga Springs to the north of Ballston Spa was a close competitor whose attractions, extended to recreational facilities and racing, gradually eclipsed those of Ballston Spa. The economic base of the latter community shifted to industrial with the advent of large mills.
In 1846, Brookside's long career as a hotel ended when the building became the Ballston Spa Institute, a school for boys. From 1859 until 1864 it served as a military academy. After the Civil War it became a private home and after that an apartment house. It is presently the headquarters of the Saratoga County Historical Society.