County population estimates for 2007: interpreting the components of change.

• Author: Thompson, Vincent

The Census Bureau's latest county population estimates paint an informative picture of population growth since Census 2000. As always, some counties gained population, some lost, and some didn't change much. It is important for us to look at changes in total county population, but some of the more interesting results won't be revealed until we dig a little deeper and examine the components of change.

The Tall and Short of It

Table 1 lists the twenty most and twenty least populated counties in Indiana, according to the Census Bureau's estimates for July 1, 2007. The top twenty counties account for 4.14 million people, or 65.3 percent of the state's estimated 6.35 million residents. Those same twenty counties only accounted for 64.3 percent of the state population as of Census 2000. That's an increase of one full percentage point for the seven-and-one-quarter year period. In contrast, the bottom twenty dipped slightly from 276,342 to 271,489 people; that is, from 4.5 percent to a 4.3 percent share of the state's population.

Looking at the changes in rank, we can see that the bottom twenty have remained relatively stable, while the top twenty have seen a good deal of movement. Notably, Hamilton County has overtaken Elkhart County at fifth place, and is on pace to overtake St. Joseph County at fourth place before Census 2010. Also, Johnson and Hendricks counties have both surpassed several other counties to fill the tenth and eleventh spots, respectively. It seems likely that Hendricks County will join the top ten soon.

Marion County, Indiana's largest county and home to Indianapolis, also makes a showing in the Census Bureau's list of 100 largest U.S. counties, placing fifty-fifth. That is a decline of five places since Census 2000, when Marion County ranked fiftieth.

To Gain or Not to Gain

Table 2 ranks the top and bottom five counties by numeric change. Hamilton County heads this list with a gain of almost 79,000 residents from April 2000 to July 2007. Although Marion County made fifth place, its growth in percentage terms ranked only thirty-seventh in the state.

Grant County sustained the greatest numeric loss of population. All of the bottom five counties have struggled with manufacturing employment losses over the period, especially Madison, Delaware, and Grant counties.

Of the top five numeric gainers, Hamilton, Hendricks, and Johnson counties also made the top five list for percent change, as shown in Table 3. All of the top five percentage gainers are "donut" counties surrounding Marion County. Two of these counties also made the Census Bureau's list of the 100 fastest growing counties across the nation: Hamilton (twenty-third) and Hendricks (eighty-fifth).

[FIGURE 1 OMITTED]

Two of the counties among the five having the greatest percentage loss, Grant and Wabash, were also among the five with the greatest numeric loss. Although Benton County takes last place here, that county is very small, so the magnitude of change was not very great; Benton County's 6.5 percent decrease corresponds to a loss of 611 residents, while Grant County's 6.2 percent decrease came with a loss of 4,556 residents.

To assess the magnitude of population growth, Figure I provides a scatterplot of percent change versus numeric change. Each of Indiana's ninety-two counties is represented by its own data point. Points that are well away from the scatterplot's "center of mass" are labeled individually. This allows us to quickly identify the counties that had the most momentum over the period. Immediately we see Hamilton and Hendricks counties have the most growth momentum, far exceeding other counties in terms of both percent and numeric change. We can also quickly determine that Grant County has the most negative momentum. Furthermore, this approach helps distinguish from the rest of the pack a few of...