7 January 2020 — 1115 mst
Prediction: the 2020 Census will report that
18 eastern Montana counties lost population
Montana’s population is growing, perhaps enough that Montana will gain a seat in the U.S. House of Representatives when Congress is reapportioned after the 2020 Census. But many areas in eastern Montana are losing population, both in absolute as well as relative terms, as western Montana becomes more populous. This will shift the locus of power in Montana’s legislature west after redistricting is completed next year.
After the Census Bureau released its estimates for state and national populations for mid-2019 at the end of last year, I extrapolated the population estimates for Montana’s counties to 1 April 2020 by assuming that each county would continue growing at the rate it grew from 2017 to 2018, a method that yields wide error bars, and plotted the projected growth of each county as a function of its 2010 Census population. I made two plots, one for all counties, one for low and negative growth counties.
Notes on the data. The Excel file contains two sheets, one with my projection to 2020, the other with the official Census Bureau estimates for 2010 through 2018. Should you want to make your own projections, these data will get you started.
There are at least as many ways to project county populations to 2020 as there are ways to calculate compound interest, all producing slightly different results. Most of those differences disappear when the numbers are rounded to the nearest hundred.
Governments — local, state, and federal — make population estimates. So do political parties, polling firms, consultants, data journalists, and academics. Not all projections are published.