According to the United States Census Bureau, the city has a total area of 1.8 square miles (4.6 km²), all of it land.
As of the census of 2000, there were 1,456 people, 560 households, and 390 families residing in the city. The population density was 815.3 people per square mile (314.1/km²). There were 609 housing units at an average density of 341.0/sq mi (131.4/km²). The racial makeup of the city was 89.01% White, 0.07% African American, 5.08% Native American, 0.14% Asian, 0.07% Pacific Islander, 2.20% from other races, and 3.43% from two or more races. Hispanic or Latino of any race were 5.43% of the population.
There were 560 households out of which 36.3% had children under the age of 18 living with them, 50.4% were married couples living together, 14.5% had a female householder with no husband present, and 30.2% were non-families. 25.4% of all households were made up of individuals and 12.0% had someone living alone who was 65 years of age or older. The average household size was 2.57 and the average family size was 3.07.
In the city the population was spread out with 28.7% under the age of 18, 8.1% from 18 to 24, 27.0% from 25 to 44, 24.0% from 45 to 64, and 12.2% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 97.0 males. For every 100 females age 18 and over, there were 91.5 males.
The median income for a household in the city was $22,991, and the median income for a family was $28,672. Males had a median income of $30,455 versus $22,250 for females. The per capita income for the city was $12,661. About 19.6% of families and 24.2% of the population were below the poverty line, including 34.0% of those under age 18 and 10.8% of those age 65 or over.
In the state legislature Montague is located in the 4th Senate District, represented by Republican Sam Aanestad, and in the 2nd Assembly District, represented by Republican Doug LaMalfa. Federally, Montague is located in California's 2nd congressional district, which has a Cook PVI of R +13 and is represented by Republican Wally Herger.