As of the 2020 United States Census, the population of Monument was 122, making it one of the smallest incorporated cities in Oregon.
The population density is quite low, reflecting the city's expansive, rural nature. The demographic makeup is predominantly White, and the community has an older median age compared to the state average, typical of many remote agricultural towns in the American West where younger generations often relocate for higher education or urban employment. The community is tight-knit, with a strong emphasis on family ties, local agriculture, and rural self-sufficiency.