Public Law 94-171, enacted in 1975, directs the U.S. Census Bureau to provide redistricting data needed by the 50 states for their use in redrawing districts of the United States Congress and state legislatures. 

Population Data - includes density, land area, and rankings

Included in the Census 2000 Public Law 94-171 tables are total population, age 18 years and over, race, Hispanic or Latino origin, and population density. Also included is land area. These are 100% data available for the state, counties, places, census designated places (CDPs), reservations, census divisions, census tracts, census block groups and census blocks. Public Law (PL) 94-171 file is the first file released from Census 2000 and is used for the Legislative Redistricting Program.

• Montana Census 2000 PL94-171 Interactive Browser
  This interactive browser provides access to total population, age 18 and over,
  under age 18, race, Hispanic origin, and population density data for all levels of
  Montana geography down to the census block level. For a brief explanation of Census 2000 geography, view the hierarchy.

See also Summary File 1 for more area and density data.