The second historic South Brooklyn congregation from which the present-day Park Slope Jewish Center evolved (after Tifereth Israel) was B'nai Jacob. PSJC's current history exhibit, "Building on a Strong Foundation," tells us:
An Orthodox group, it erected a synagogue in 1898 at 136 Prospect Ave., between 3rd and 4th Avenues. The building cost $8,500 and seated 350. New York Mayor Van Wyck and other officials joined in the cornerstone-laying, as did the rabbi of Beth Elohim.
According to the exhibit, B'nai Jacob (together with B'nai Sholaum, another ancestor of PSJC) facilitated the creation of a YMHA that once stood at 345 9th Street, between 5th and 6th Avenues:
In 1906 a Hebrew Young Men's Institute of Brooklyn was formed. (The initial meeting was held at B'nai Jacob.) The group purchased 345 9th Street, and the Y opened the following year. The first successful YMHA in Brooklyn, it was closely affiliated with B'nai Sholaum. The Y's baseball teams played at the Parade Grounds, and its dramatics program was led by Moss Hart. In the 1930s the Y moved to 339 8th Street, the building that now houses Camp Friendship.
The original building at 345 9th Street was approximately where the 9th Street CVS now stands:
The Camp Friendship building, where the YMHA met in the 1930s, was erected in 1884 as the Sixth Avenue Methodist Church (later to become the Park Slope United Methodist Church):
PSJC's exhibit informs us of Congregation B'nai Jacob's ultimate fate:
B'nai Jacob was small. It grew steadily from 75 members in 1908 to 115 by 1925. But the property was condemned in 1942 to make way for the Prospect Expressway. The congregation merged with Tifereth Israel that same year.
Ouch! B'nai Jacob's even-numbered address (#136) would have placed it on the south side of Prospect Avenue, between 3rd & 4th Avenues. As can be seen from the photo below, only the north side of Prospect Avenue still stands; the south side of that block was lost to one of Robert Moses's contributions to Park Slope, the Prospect Expressway:
Thus Congregation B'nai Jacob merged with Congregation Tifereth Israel in 1942 to create the new, consolidated Congregation B'nai Jacob Tifereth Israel.
Up next: Congregation B'nai Sholaum.