The Mill River flood of 1874 was one of the great man-made disasters of late nineteenth century western Massachusetts. Early in the century, the combination of high hills and rapid water encouraged the construction of a string of mills up and down the Mill River Valley, with as many as six mill villages rising up to take advantage of the cheap and abundant source of power. Factories for the production of silk and woolen cloth, buttons, brass and iron, and a variety of other products lined the banks of the river, supporting a growing population of workers.

By the 1860s, mill owners began to recognize that the natural, seasonal variation in water level in the Mill River could be evened out by damming the river, and in 1864, they began work on constructing a large earthenwork dam just above the town of Williamsburgh. Weighing the cost of the project, however, they decided to economize by designing and building the dam themselves, and cutting further corners and cost during the actual construction. Despite complaints from the surveyor and workers that these measures were potentially compromising to public safety, work continued, and even the presence of leaks when the dam was first filled in 1866 did little to slow the project.

Following heavy rains on May 16, 1874, disaster struck. When the dam collapsed, 600,000,000 gallons were sent coursing downstream in a wall of water nearly 40 feet high in places. Despite efforts to warn the residents downstream, few heard the warning, and fewer still heeded it. When the waters finally subsided, 139 bodies were strewn in its wake, with nearly total devastation of the factories and homes, bridges and roads.

In following days and weeks, the state government, for one of the few times in its history, stepped in to lend $120,000 assistance to rebuild the infrastructure, and despite a coroner's inquest that laid clear culpability for the disaster on the shoulders of the mill owners and engineers, no one was ever brought to account.