As of the census of 2000, there were 500 people, 230 households, and 58 families residing in the CDP. The population density was 98.8 people per square mile. There were 65 housing units at an average density of 35.8 per square mile. The racial makeup of the CDP was 96.95% White, 2.29% Native American, and 0.76% from two or more races. There were 58 households out of which 27.6% had children under the age of 18 living with them, 53.4% were married couplesliving together, 5.2% had a female householder with no husband present, and 36.2% were non-families. 31.0% of all households were made up of individuals and 8.6% had someone living alone who was 65 years of age or older. The average household size was 2.26 and the average family size was 2.84. In the CDP, the population was spread out with 26.0% under the age of 18, 5.3% from 18 to 24, 23.7% from 25 to 44, 27.5% from 45 to 64, and 17.6% who were 65 years of age or older. The median age was 39 years. For every 100 females, there were 92.6 males. For every 100 females age 18 and over, there were 94.0 males. The median income for a household in the CDP was $25,357, and the median income for a family was $28,750. Males had a median income of $24,583 versus $19,531 for females. The per capita income for the CDP was $14,647. There were 13.5% of families and 10.2% of the population living below the poverty line, including 14.7% of under eighteens and 14.3% of those over 64.
History
The town is named after the Sun River, by which it is located. The name was from the Indian word Nataeosueti, translated by the English as "Medicine" or "Sun" river. Artifacts have been found in the area related to native cultures dating back to 2000 B.C.. More recent Native tribes included the Blackfeet and Crows.
Climate
Like most of Montana outside of the highest mountains, Sun River has a cold semi-arid climate characterised by hot summers with chilly nights, and cold winters with very high temperature variability due to warming by chinook winds contrasting with occasional severe chilling by polar air from Canada. During winter, maximum temperatures exceed on an average of 18.4 days between December and February, and a total of 26.7 days in November and March. During cold outbreaks minima fall below on 25.5 nights in an average winter, though only seven such nights occurred during the very mild winter of 1999–2000 but as many as fifty-two in the cold winter of 1968–69. In the summer temperature exceed on 14.2 days, although is exceeded merely once in five summers on average. Most precipitation comes from thunderstorms in late spring and summer, but even then it is less heavy than further into the Plains. The wettest recorded month has been May 1953 with, whilst in September 2012 not even a “trace” was reported. Snowfall is moderate due to the dry winters, with a mean of and a median of. The most snow in a month has been in April 1967, whilst the most snow on the ground has been on 17 February 1959 following a storm depositing over the previous two days.
