In 1957, a group of friends started an informal Wednesday evening discussion group. Many of these individuals were scientists from the Brookhaven National Lab in Upton, Long Island. At first the group met in individual's homes. As interest in the group increased, members started advertising their existence in local newspapers and began using the YMCA building in Patchogue Village for meetings. The members began to see a need for some kind of religious education for their children and on doing some research themselves, decided that Unitarianism fit in well with their humanist bent. The name "Unitarian Fellowship of Brookhaven" was adopted.

By 1960, the Unitarian Fellowship of Brookhaven began to investigate establishing it's own meeting space. Funds were raised and they got an offer to buy the house and property on Browns Lane in Bellport Village. By January 1961, with the transaction complete and the advent of the merger of Unitarians and Universalists, the membership voted to change the name from the Unitarian Fellowship of Brookhaven to the Unitarian Universalist Fellowship of Bellport.

The building itself was built in 1857 with many additions along the way. The main part of the building was a two-story frame building. At some point, the front and side porches were added and then closed in. A carriage house was constructed and the property once had a windmill, which has been torn down. In the early 1900's a large "ballroom" was constructed on the north side of the main building exclusively for the daughter of the owner on the occasion of her wedding. Today this serves of the Fellowship's sanctuary. The Fellowship currently rents the "carriage house" on a yearly basis and an attached apartment seasonally.

The Fellowship has a strong Humanist history, due largely to fact that so many of it's founding members worked at either the State University at Stony Brook or the Brookhaven National Lab. Sunday "programs" were largely informational in nature and lay led. Religious Education was important and vibrant with enrollment topping out at 30+ children and youth. During the Vietnam war years, the Fellowship was a strong liberal voice for the opposition and its members participated in many anti-war protests. Throughout its history, the Unitarian Universalist Fellowship of Bellport's members have been very involved in many varied social action projects and have been at the forefront of the drive for affordable fair housing for the people of the Bellport area.

UUF Bellport has a long history of being proudly lay led. While it has been reported that there was a minister on staff for a short time, records of this have not been located. Interviews with long time members report that this one attempt was short lived due to the "do it yourself" attitude and strong belief in congregational polity. From the beginning, UUFB has had a very independent, can-do spirit.

The late 1980's saw some decline in membership as the founding members and their children got older but the early 1990's saw some increase. With the influx of newer, younger members to the Fellowship, there has been an increase in interest in a more "spiritual" intentional Sunday service, a moving away from the intellectual discussions toward thoughtfulness about our identity as humans and as Unitarian Universalists.