Peoria’s Chamber is still rounding down or not really counting the whole CSA or something.

Peoria’s CSA is made up of the Peoria MSA + Fulton County.

Google “Fulton County IL population” and the inset from Google, from the Census Bureau, will tell you the year 2019 estimated population is 34,340.

Wikipedia says the year 2019 estimated population for the Peoria MSA is 400,561.

Add the two together and you get 434,901 as the 2019 estimated population of the Peoria Combined Statistical Area. I can’t find a place that flat-out says “here’s the estimated 2019 Peoria CSA population” because populations aren’t estimated for everything in non-census years, but it is easy to calculate.