In the summer of 2000, Hamilton made international headlines when forest fires throughout the Bitterroot Valley filled the area with smoke and prompted the evacuation of many residents. President Clinton declared a state of emergency in the area and dispatched National Guardsmen to assist with fighting the fires.
Hamilton is, as of 2004, home to two microbiological research and production facilities: the government-run Rocky Mountain Laboratories, and a branch of the Corixa Corporation (bought in the late 1990s from Ribi ImmunoChem Research, Inc.). The Corixa Corporation was bought by GlaxoSmithKline in 2005. In the early 2000s, the government began a case study of the possibility of constructing a Level 4 biohazard laboratory in the Rocky Mountain Laboratories facility, which would be one of two civilian-run Bio-Safety Level 4 labs in the United States (all others are operated by military personnel). Although met with much local opposition, the facility is currently being constructed.
According to the United States Census Bureau, the city has a total area of 2.3 square miles (6.0 km²), all of it land.
There were 1,772 households out of which 22.3% had children under the age of 18 living with them, 36.3% were married couples living together, 9.5% had a female householder with no husband present, and 51.7% were non-families. 47.6% of all households were made up of individuals and 24.9% had someone living alone who was 65 years of age or older. The average household size was 1.95 and the average family size was 2.81.
In the city the population was spread out with 20.2% under the age of 18, 6.8% from 18 to 24, 24.0% from 25 to 44, 20.6% from 45 to 64, and 28.3% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 82.2 males. For every 100 females age 18 and over, there were 74.9 males.
The median income for a household in the city was $22,013, and the median income for a family was $30,665. Males had a median income of $25,795 versus $22,138 for females. The per capita income for the city was $14,689. About 14.3% of families and 17.8% of the population were below the poverty line, including 28.4% of those under age 18 and 15.3% of those age 65 or over.