In yesterday’s post I discussed the need for population growth in Chicago and the timing couldn’t have been better—or worse; I can’t decide. That’s because the U.S. Census released figures later in the day showing the city’s population fell by 200,000 souls since the year 2000.

That’s a 7 percent drop. And in contrast to the white-flight that reduced the city’s population by 600,000 between 1960 and 1980, it is now African Americans who are leaving the city in large numbers. The black population in Chicago went from 1.065 million in 2000 to 888,000 now.

With a population of 2,695,598, according to the 2010 U.S. Census, the city is a hair smaller now than it was in 1920. The population was 2.7 million then and would grow by almost a million over the next 30 years before begining its decline, falling from the nation’s second largest city to its third.

But could we someday fall to number 4?

New census figures for Houston have not been released as of this writing, but I am curious about what numbers they could tell. The Texas city was the nation’s 45th largest in 1920 and has sat at number 4—right behind Chicago—since 1990. Houston’s population was 1.6 million in 1990 and grew to 2.25 million according to an current-day estimate on the state of Texas’ website. Actual census figures, when released, would reveal a truer population spread between the two cities. It might be unlikely Houston will catch us in population now, but if that city’s growth and our population decline continues, Chicago might well be the 4th largest city in 2020.

This is critical issue for Chicago—or it should be. And its not about bragging rights over size either. A shrinking city is ultimately a decaying city, and one that becomes increasingly expensive to sustain and even harder to redevelop. Catch the Metra Rock Island southward from the LaSalle Street station, if you get a chance, and you’ll see vast amounts of vacant land along the line. Neighborhoods just cored out by the acre from 47th to near 67th—quite reflective of the population losses reported in the census. How do we fix that?  And when?

It is time for a plan—and it is a perfect issue for a new mayor—that identifies and sets up ways and incentives to substanially grow Chicago’s population throughout the city over the next 25 to 50 years. Without some kind of effort like this, the population won’t stay stagnant; the 2010 census figures show that population will instead ebb. And if that loss persists, it will likely take with it much of spirit and energy that made this city great.

If Chicago is to remain a city of sigificance, the time for action is now.