[OldHand2018]

Chicago used to have extremely high industrial employment, so the general downward trend across the United States was amplified in Chicago. The population peaked in the late 1950s and has been dropping since, although the rate of decrease has been dropping as Chicago has transitioned to a very diversified economy. The north side of the city is now very stable population-wise and the downtown area has seen incredible growth (in the last 3 censuses, Chicago has seen higher downtown population growth than any other city in the US), while the south and west sides continue to struggle. These are the areas that were the most industrial.

Houston has seen tremendous growth primarily through annexation. It is now more than 3 times the geographical size of Chicago. But annexation of residential land in Texas is now far more difficult, so the geographic size growth of Houston has dramatically slowed [1]. Once all the undeveloped land is used, Houston will have to rely on densifying for population growth. Current restrictions make it unlikely to ever be as dense as NYC, Chicago or LA, but with its massive size it wouldn't need to be to attain 5 or 6 million residents. On the other hand, it is already facing growth challenges that may reduce the carrying capacity of the city [2].

I'd guess that Houston surpasses Chicago in population within 15 or 20 years, but it remains to be seen if that is going to be permanent or not.

[1] https://www.houstontx.gov/planning/Annexation/docs_pdfs/Hous...

[2] https://www.houstonchronicle.com/news/transportation/article...