County Population Changes are a Mixed Bag

March 28th, 2016

This week we look at the recently released population data for U.S. counties. We also look at potential causes for the decline in population in Cook County, Illinois.

County Population Changes are a Mixed Bag

Last week the Census Bureau released population estimates for counties for 2015.

The largest gainers were Harris County, Texas (+90k), Maricopa, Arizona (+78k), and Los Angeles, California (+61k).  The biggest losers were Cook, Illinois (-10k), Wayne, Michigan (-7k), and Cuyahoga, Ohio (-5k).

A difficult aspect of analyzing the change in county populations is that county sizes differ dramatically, both in population and land area.

Los Angeles has the largest population of any county in the country. It is home to more than twice as many people as Cook, Harris and Maricopa.


For both the gainers and the losers the change during 2015 was a continuation of long-term trends.  Maricopa and Harris have experienced steady population growth over the last 25 years.  Cook’s population has been stagnant.  The population has been shrinking in Wayne and Cuyahoga.

The following chart puts the 2015 population changes in a national perspective.


The chart compares each county’s share of the U.S. population (x-axis) to its contribution to U.S. population growth during 2015 (y-axis).  Counties falling on the grey line are growing at the same rate as the U.S. overall.  Counties below the line are lagging U.S. growth, and counties above the line are growing faster.

While Los Angeles in lagging, nearby counties of Riverside and San Diego are growing faster than national averages.

California Population Growth by County (2014 to 2015)


Source:  U. S. Census Bureau, DIVER Analytics

Other notable counties in California with strong growth are Yolo (+1.8%), Alameda (+1.6%), San Joaquin (+1.5%) and San Francisco (+1.4%).

Cook County Decline Attributed to Several Factors

The decline in Cook County’s population received wide coverage in both local and national news outlets.

Reactions varied by political leanings.  The vocal anti-tax/anti-regulation groups in Chicago attributed the decline to companies and individuals leaving to escape rising tax and regulatory burdens.  This political cartoon from the advocacy group Illinois Policy most colorfully represents this view.


Source:  Illinois Policy

Illinois Policy supports this thesis with statistics that show that net migration was a large drag last year.

A look at our sample of winners and losers for 2015 supports this view.


Cook County lost a higher percentage of its population (-0.6%) than the other counties.

An article in the Chicago Magazine acknowledges that net migration was a factor, but emphasizes the impact of  Chicago’s relatively weak ratio of births to deaths.


The data is not as supportive of the role of births and deaths.  Growth due to births/deaths is positive in Cook  (+0.53%) and while weaker than the leaders, only slightly trails Los Angeles (+0.65%) and Maricopa (+0.64%).

Whatever the source, if the decline in population continues, it will make solutions to Chicago’s (and Illinois’s) fiscal problems more difficult, especially if the decline in population is driven by a desire to escape the tax burden.


Have a Great Week,

Michael Craft, CFA