Regarding Marion County, it is also worth considering that only a sliver over half of the population resides in incorporated Salem. On the other hand, 60% of Lane County's population lives in Eugene or Springfield, and 63% of Benton County's population is within the bounds of incorporated Corvallis.
Yeah, I noticed that when I did those 100K districts. Outer Lane county is pretty much empty. Marion County has people everywhere. I wonder actually if the area can be reasonably described (in parts) as being far exurban Portland - which would of course also explain why it votes Republican.
