Today, in the History Room at the library, I consulted a 1928 Sanborn Map and discovered that the corner of Union and First streets was already vacant at that time, except for the building that still stands (for now) on First Street at Cherry Alley. So what happened to the buildings that faced Union Street?
This article from the Hudson Evening Register for July 8, 1911, explains it all.
TWO HOURS' FIRE FIGHT
Fire in the Old Wagon Shop
Property on First Street.
STARTED IN STABLE PART
Portion of the Old Wooden Struc-
ture Toward Cherry Alley
Shortly after 3:30 o'clock this morning flames were detected issuing from the hay mow and old wagon shop of the stables, situated on First street, between Cherry alley and Union street, owned by Benjamin Propst, who conducts a blacksmith shop at Union and First streets. The fire was in the part used by Jacob Krasner, the North Front street grocer. An alarm was immediately sounded, but before the firemen arrived, the flames, fanned by a northern breeze, had gained much headway in the wooden structures and were spreading rapidly.
The fire was a spectacular one, and the flames illuminated the sky for blocks, which to up-town people produced an effect as if the whole lower end of the city was enveloped in flames, apparently, and in a few minutes hundreds of excited people had assembled about the burning buildings.
When the first stream was turned on by the firemen, the flames had already swept through the wagon shed, which adjoins the stables and were eating their way into the next adjoining apartment, which for the past few years has been used as the polling place for the First Ward. In the stables Mr. Krasner had three horses tied. Two of the animals broke their halters and dashed out of the burning building, when the streams were turned on it. The other animal remained in its stall some time, being finally brought out by its owner. The flames in the stable were quickly extinguished, as the firemen could get at them easily, but the situation of the other parts of the property proved inconvenient to the department in their efforts to check the flames from spreading toward Union street.
The shed annexing the stables was totally destroyed, while the storehouse next to the shed was practically consumed. After a two hours' battle the flames were subdued, as they as entered the polling room. The firemen are to be congratulated upon the excellent service they rendered in preventing the flames from spreading to the residences nearby.
The origin of the fire cannot be ascertained, but it is believed to have been the work of an incendiary. The loss is estimated at $1,500, covered partly by insurance. According to residents in that vicinity several strange men have been seen lately to enter the hay mow and polling house during the night and last evening a young down-town man was asleep in the polling house when the fire was discovered.
This advertisement from the Evening Register for May 27, 1870, provides evidence that a shop where carriages and wagons were built and repaired had been located at Union and First streets for several decades.