* Age 0-9 only.

How we used this Census data –

For this study, Southern Illinois is limited to the southernmost thirteen counties in Illinois, which include Alexander, Franklin, Gallatin, Hardin, Jackson, Johnson, Massac, Perry, Pope, Pulaski, Saline, Union, and Williamson counties.

The population was tracked by ten-year age groups, not accounting for deaths, migration patterns, etc. In order words, all the babies born in the 1920’s would be grouped in the 0-9 age group when the 1930 Census was taken. This ten-year age group, or ten-year "generation", was tracked by each subsequent Census count, for example, in the 1940 Census the babies born in the 1920’s would be represented by the 10-19 age group, in the 1950 Census by the 20-29 age group, etc.

Our Census data charts, therefore, group the population in age groups from age 0-9, 10-19, 20-29, 30-39, 40-49, etc. in order to easily track each generation of babies born every ten years and how their numbers changed as they reached the age groups we wished to study, disregarding deaths and migration patterns in or out of the region.

Unfortunately, the Census data we obtained does not always group data into the ten-year age groups we required for this study. Often the Census Bureau would indicate population age groups using mid-decade ages (i.e., age 45-54, age 55-64, etc.) When ages from the Census were ranged from mid-decade to mid-decade, that figure was divided in half and each half was redistributed between the age ranges we needed for this study. When the dividend resulted in a fraction, the younger age range was increased and the older age range was decreased in order to bring them each to a whole number. Therefore, some statistical error may have been introduced as a result of our methods, however, the overall trends we found probably were not affected.

The 1930 Census data was the first we found which grouped the Census count by county and age groups. The Census data that is available to us prior to 1930 require us to hand-count the number of individuals in each age group in every county. We decided not to pursue this labor-intensive count with the pre-1930 Census data.

We did, however, find a source for the 1920 Census which indicated age groups by county for ages 0-6 and ages 7-13. We used this data to determine the number of individuals in the 0-9 age group for each of our counties for the 1920 Census. In order to do this we added the number of individuals aged 0-6 to a percentage (3/7^ths or 42.8571 percent) of those in the 7-13 age group. We did not try to determine the data for any other age group for the 1920 Census.

On the county census data sheets, formulas may actually vary somewhat from county to county and decade to decade based on how federal census reflected age brackets and whether or not there were fractions resulting from dividing age ranges.