Of course, there are probably more important foundational anniversaries in Longmont history, like the day that the colony organized in Chicago (November 22, 1870) , or when this area was selected by the location committee (late January 1871), or the day the colony was incorporated in Colorado (February 2, 1871). But today's March 9 date seems like a very accessible birthday to celebrate just because we see and use our city name so many times a day.
It would be interesting to know what other names were being considered.
A March 3, 1871 article about the Chicago-Colony in the Rocky Mountain News described the area now known as Longmont:
"The scenery combines the beautiful, the grand, and the picturesque, while the climate is favorable in every particular."and correctly predicted the end of the village of Burlington (1861-1871), down by the river:
"The hitherto flourishing little point of Burlington will doubtless become extinct by joining the fortunes of the now city, whose name has not yet been determined upon."Six days after this was published, a name was chosen.
A good reference for the early years of the Chicago Colony is: "The Founding and First Year of Longmont, Colorado" by Howard K. Phillips, Jr. (1974). This was actually a term paper before it was bound into a book, and it's available at the Longmont Library.