However, Hamilton's prosperity was not to last. It was soon discovered that the local ore deposits proved shallow. Subsequently, by 1870, less than two years after its founding, the community was already in decline. Once the shallow nature of the local ore deposits became known, many of the mining companies left the area. Hamilton's population and economy began a rapid decline. At the census of 1870, the population was 3,915, less than a third of what it had been estimated at the previous summer. On June 27, 1873, a large fire spread throughout the business district and caused an estimated in damage. Most businesses that burnt down were abandoned, and not rebuilt. By this time, the town's population was estimated to have shrunk to only 500. Another fire destroyed the courthouse at Hamilton along with all of the records in January 1885. County records began to be kept at the Ely courthouse begin January 5, 1885.