Though today it stands in the town of White Sulphur Springs, the Union League of America Hall is older than that town by several years. The hall was built in 1867 by the Union League of America and moved to White Sulphur Springs in 1881 by the Diamond Lodge No. 5 of the Independent Order of Good Templars.
One of the state's richest gold strikes in the early prospecting days of Montana occurred in Confederate Gulch, twenty-five miles west of White Sulphur Springs. The Confederate Gulch strike led to the creation of Diamond City, which came to be known as one of the toughest places in Montana. By 1867, the year this hall was built, Diamond boasted a population of 5000 people. That was also the year in which Meagher County, of which White Sulphur Springs is the county seat, was created. Though Diamond City was the original county seat, it was replaced by White Sulphur Springs in 1880, as the former shrank and the latter grew. By 1875 the Union League of America had faded away in Diamond City and the building was sold into private hands by 1875. In that same year it was purchased by the Independent Order of Good Templars.
The townsite of White Sulphur Springs was platted in 1878, a post office having been established there in 1876. The first commercial building we know of in the town, the
Wellman Block, wasn't built until about 1880. Given that the hall was built 11 years before the platting of the town, it is, by a minimum of 10 years, the oldest building in White Sulphur Springs.
Seven years after the Independent Order of Good Templars moved the building to White Sulphur Springs, financial difficulties forced its sale to the Presbyterian Church. The church renovated the building, repurposing it as a church. It remained in the hands of the Presbyterian church until 1971, at which time it transferred ownership of the Union League of America Hall to the Meagher County Historical Association. The building has been, for the most part, vacant since that time.