And supposedly half the population that lives West of the Mississippi lives within 30 miles of I-5. Don't have the US Census loaded currently so I can't check it, but that does sound about right.

Given that half the population of the US is 156 million, and half that is 78, it's plausible, but a quick add-up of combined MSAs comes up short:

LA is 18.1 million, San Diego 3.2 Sacramento 2.2, Stockton 0.7, Portland 0.5, and Seattle-Tacoma 3.6. I get about 23.3 million total, which is still 54 million short.

SF-SJ-Oak adds another 8.4 million, but most of it is more than 30 miles from I5.

Checking by state confirms it:

CA: 38m, OR: 3.9m, WA: 6.9m. combined total: 48.8m. Still 30 million short.

Mythbusted.

Actually, west of the mississippi (and assuming all of Louisiana and Minnesota) the population is only about 130 million - so those three states are about 40% of that population. Given the rapid growth of texas, colorado and arizona, and Nevada (well Las Vegas) in the last 15 years, it wouldn't surprise me if those three states would have been over half the population west of the Mississippi not that long ago.

As for within 5 Miles of I-5.. probably not, but within it's area of influence, for sure - the western parts of those three states are pretty empty, even by my midwest trained standards.

It was 30 miles, not 5 (HN's reply windows makes back-references while composing difficult, I'll grant you that).

And yes, as an old / dated statistic, a 30 - 100 mile radius might have worked further back.

Truth is that population centers are highly concentrated within the US (and the world).

A set of visualizations I've collected showing density as cartograms or height relief: http://imgur.com/a/JgtVp#0

The height map in particular shows the concentration by MSA, and the population density of the eastern US: http://i.imgur.com/NjeWb3a.png

Incidentally, I'd always thought it was 2/3 of the US population east of the Mississippi. Yep.

Adding up: ca: 37.2, or: 3.8, wa: 7.0, id: 1.6, mn: 1.0, nv: 2.8, az: 6.6, ut: 2.9, wy: 0.6, co: 5.3, nm: 2.0, tx: 26.4, nd: 0.7, sd: 0.8, nb: 1.9, ks: 2.9, ok: 3.8, mn: 5.4, ia: 3.1, mo: 6.0, ar: 3.0, la: 4.6, ak: 0.7, hi: 1.4

We get 131.5 million. US pop: 313m

Via bc:

    100 * (131.5/313)
    42.000

Leaving 58% on the east. Not quite 2/3, but close.

Knock off Texas and you're there: 105m, or 33.546% of the US population.

Last I checked, most of Texas was more than 30 miles from US I-5. Or even more than five miles.

Using 2010 census numbers from http://en.wikipedia.org/wiki/Us_state_population, rounded to nearest 100k.