3 districts for Idaho – a look ahead to 2020 redistricting?

Idaho has, as Nathaniel90 put it, a shot at “the prize of least interesting congressional redistricting process of the decade.” The current ID-1 and ID-2 are R+18 and R+17 and the minor revisions they’ll receive will not change this to any great extent.

On the other hand, at current growth rates there’s an outside chance that Idaho will receive a third congressional district after 2020, and almost certainly after 2030. And that’s where things get interesting.

Idaho is a fast-growing state. 6 counties saw growth of above 25% between April 2000 and July 2009, including the three largest counties of Ada, Canyon and Kootenai and for the state as a whole population increased by an impressive 19.5%.

But this growth is unevenly distributed, being much more notable in urban than in rural counties, higher in the Panhandle than in central and eastern Idaho and highest of all in the Boise-Nampa Metropolitan area in south-western Idaho.

Given that the growth is here and that the area will contain around half the state’s population, it’d be natural to locate a third congressional district here.

Republicans would be unlikely to be keen, as whilst McCain won all but 3 small counties in the state, Obama’s next best county was the state’s biggest, Boise. If portions of this were combined with (the admittedly very conservative) fast-growing Canyon County to its north-west, you’d have a district a garden-variety of insane Republican could lose and not just a Bill Sali kind of insane Republican.

Yet whilst Republicans dominate the state, Idaho opted for bipartisan redistricting in the 1990s. Democrats and Republicans both name three representatives to a commission that draws the maps and with Republicans often divided between the lunatic fringe and more mainstream conservatives, Democratic power on the commission is even more disproportionate to their popular support than the numbers would suggest.

I therefore suggest than if Idaho receives a third seat in 2020, the commission will draw a very compact Boise-Meridian-Nampa-Caldwell district that would rival WA-7 as the smallest district in the northwest. This would likely be a fair fight district, and in retaliation Republicans would almost certainly try to reintroduce partisan redistricting.

Read on for the districts themselves and methodology.

To estimate the 2020 population of Idaho and its distribution, I took the April 2000 population of each county. I then recorded its growth up to July 2009 (as the 2010 numbers aren’t yet out) and extrapolated this out to April 2020.

I only split two counties, namely Ada and Canyon, but here I encountered some problems. The city of Boise itself has enjoyed only modest growth, whereas other cities have nearly doubled in size in the past decade. It’s unlikely this will be allowed to continue unimpeded for another decade, but by the same token other smaller cities will be likely to experience explosive growth.

Rather than trying to model this, I took the cop-out option of working out what proportion of the two counties I needed to draw into other districts to achieve population equality, then removing them based on the population in Dave’s Redistricting App. This is not a rigorous method and will undoubtedly be out by several thousand in the final analysis, but it did at least allow a rough picture of the likely districts to be drawn.

Idaho with 3 CDs


2000 population: 466396

Estimated current population: 524907

Estimated 2020 population: 614623

This district combines the Idaho panhandle with most of the Treasure Valley and a couple of rural counties thrown in for population equality.

It’s slightly oversized because it made the mental arithmetic slightly easier, but moving one block group would fix that and there are plenty of suitable ones around Boise.

Guaranteed safe Republican.


2000 population: 360291

Estimated current population: 486060

Estimated 2020 population: 610485

From Boise in north-central Ada County this heads west along I-84 (west) until Caldwell, taking in Meridian and Nampa along the way. For the most part the Boise River is the northern boundary, but it heads beyond that to take in northern parts of the capital as well as the town of Eagle.

As the scale shows, it’s probably only around 200 square miles and hence takes up less than a quarter of a percent of the state’s land area.

Probably leans Republican, but a lot less so than the other two districts.


2000 population: 467289

Estimated current population: 534835

Estimated 2020 population: 613230

This district fits communities of interest surprisingly well, as it takes in all of eastern Idaho and the Magic Valley as well as the Wood River Valley.

It would also include the rest of central Idaho, but I had to remove Custer and Lemhi counties to ID-1 for population reasons. This is a shame, as they have no road connections in that direction. However, if, as seems likely, population in rural eastern counties continues to decline, it might be possible to include them in this district in a 2020 map.

Would be monolithically Republican, even if it wasn’t even more Mormon than the present ID-2 already is.