Migration Drives South Dakota Population Growth
After a long climb to finally recover to its 1930 population in 1990, South Dakota’s population has risen significantly to just over 900,000 in 2022. Most recently, between July 2021 and July 2022, South Dakota grew at an impressive 1.52 per cent, placing the state fifth in the nation behind Florida, Idaho, South Carolina, and Texas. This report summarizes growth since 2000, looking at overall trends and components of growth and placing South Dakota’s experience into context by comparing it to the nation and neighboring states.
South Dakota Population and Growth
Figure 1 shows South Dakota’s annual population since 2000. The numbers are the July 1 annual estimates from the Census Bureau. Population has grown each year since 2000, with a fairly steady growth path that hides some differences in rates from year to year. The growth seen in South Dakota is shared by many neighboring states. The time trend for South Dakota and the surrounding states with the most similar population is shown in Figure 2. Montana exhibits a very similar growth path, while North Dakota and Wyoming have had periods of both no growth and relatively rapid growth associated with energy production.
South Dakota’s annual growth rates are shown in Figure 3 compared to the United States. The rates vary from a low just above zero between 2019 and 2020 to a high of about 1.5% between 2021 and 2022. The 2010 and 2020 census years most likely reflect the data ‘anomaly’ of the actual count in April of those years, which can differ from the estimated trend, along with real changes around the census year. A better view of the trends in population change is provided in Figure 4, where five year smoothing is employed to address the census effect and any other year-to-year estimation errors. The smoothed curves reveal that South Dakota’s growth rate caught up to the national rate around 2005 and has been higher than the national rate since 2010. The current smoothed rate in South Dakota is about half again the national rate, while the estimated 2021-2022 rate of 1.52% is four times the national population growth rate.
When the South Dakota smoothed growth rates are compared to the state’s eastern and southern neighbors, higher growth in South Dakota is apparent. As shown in Figure 5, South Dakota’s growth rate was higher than Minnesota’s, Iowa’s, and Nebraska’s in most years. Minnesota had comparable growth early in the time period but has remained flat, while Iowa and Nebraska started with lower rates (lowest in Iowa), rose to higher rates for a few years on each side of 2010, and then fell back to their previously lower rates.
Across the entire time span, South Dakota’s population grew by 20.4%, while the nation grew at 18.1% and the Census Midwest Region grew at only 6.7%. Montana and North Dakota had slightly higher cumulative growth rates, with Montana seeing somewhat higher and North Dakota somewhat lower recent growth than South Dakota. Minnesota, Nebraska, and Wyoming had growth rates between about 15% and 18%, all below the national average, while Iowa grew by 9.3%.
Components of Change
The sources of growth provide a fascinating look at the mechanism generating the recent population growth. Change over time in population is typically viewed through the Demographic Equation:
Popt+1 = Popt + Births – Deaths + Net Migration. Following the Census Bureau designation, we will examine domestic migration and international migration separately. The data and figures omit the 2009 – 2010 changes, which are not reported with other years in the Census data files.
Birth data is provided by states to the Centers for Disease Control, which in turn publishes data for all states and provides counts to the Census Bureau for use in population estimation. The birth counts for South Dakota are shown in Figure 6. South Dakota experienced growth in births from 2000 to 2007, followed by minor variation for several years, and then a slight decrease, including a notable drop in 2020-2021 likely due to the pandemic.
Figure 7 presents the births as a percentage of the prior annual population estimate and compares South Dakota to the US and surrounding states. This measure, related to the “crude birth rate” which involves dividing by 1000 (instead of 100 for these percentages) and deemed crude because it uses the entire population rather than women in child-bearing years, reveals that South Dakota experienced an increase until 2007 and then an uneven decrease until 2022 which left the rate 0.1% lower than the initial rate. Nebraska followed a very similar trend, while North Dakota experienced a very pronounced increase up to 2015 followed by a decrease that still left its rate highest in the nation. Minnesota and the nation as a whole started with a rate similar to South Dakota, but their rates fell throughout the time period and sit significantly lower than South Dakota, Nebraska, and North Dakota.
While the birth percentage relates directly to population change, a more interesting view is provided by the total fertility rate (TFR), which uses births rates computed by age cohorts of women to derive an estimate of how many children a typical woman will have. Total fertility rates for several states and the US are shown in Figure 8. South Dakota’s TFR was one of the nation’s highest in 2008, and, despite dropping over the time period, is currently the highest in the nation. South Dakota is the only state to have a TFR close to the replacement rate of 2.1 children/woman. South Dakota’s TFR exceeded the US TFR by 0.28 in 2008 and by 0.41 in 2021. It is almost half again the TFR of Vermont, the country’s lowest state. While South Dakota’s TFR dropped less than the nation and far less than Utah, the 2008 leader, it’s drop is comparable to that in neighboring states.
Annual deaths stayed between 6,782 and 8,015 from 2000 through 2019 before shooting up nearly 25% to 9,867 in 2020-2021 and remaining at a relatively high 9,231 in 2021-2022. In every year (including the Covid-19 years), births exceeded deaths, leading to natural increase. Death rates as a percentage of population stayed fairly consistent until 2018-19, at which time all states and the nation rose dramatically through 2021. South Dakota’s rates were higher than the US rates until a brief period of lower rates from 2018-2020, but they jumped above the national rates in 2020-21 before dropping to match the national rate in 2021-22. Regionally, South Dakota’s death rate has generally stayed between the lower rates in Minnesota and the higher rates in Iowa.
Domestic migration is of elevated interest in the analysis of state population, as it provides a measure of the relative attractiveness of states. South Dakota (Figure 11) has experienced mostly positive net migration across the time period, with significant negative net migration only in the first two years and in 2014-15. Net migration was very slightly negative in 2019-20. The period between 2005 and 2013 was a significant net inmigration period. The most notable inmigration has occurred in the two most recent years, where a net inmigration of more than 6,000 new residents occurred each year.
Net domestic inmigration rates as a percentage of state population and comparison to selected surrounding states are shown in Figure 12. South Dakota has outperformed the neighboring states in virtually every year since 2003. For most of the time period, Iowa, Nebraska, and Minnesota had net outmigration (negative net inmigration), with Iowa and Nebraska’s worst years around 2000 and Minnesota’s in the most recent two years.
International migration does not share the same “competitive” interpretation as domestic migration rates, but it can still be an informative and important component of population change. South Dakota’s international migration (Figure 13) fluctuates significantly from year to year, with a clear increase in the average level in more recent years. The peak year was 2016-17 with close to 4,000 immigrants, although as recently as 2017-18 South Dakota had fewer than 700 immigrants.
When rates are examined and compared to the nation and surrounding states (Figure 14), the volatility of South Dakota’s international migration is even more pronounced. South Dakota clearly lagged behind neighboring states in the earlier half of the time period, but its rates were more comparable, while extremely variable, in the second half. In the most recent several years, South Dakota international migration rates were very similar to both the US and surrounding states and were actually slightly higher.
When all of the components of population change are considered, it is apparent why the state has grown so rapidly recently. Both natural increase, including being the only state with a birth rate close to replacement level, and exceptional domestic migration in addition to strong international migration, have generated notable growth. If the growth since 2020 continues throughout the remainder of the decade, South Dakota could near the one million threshold by 2030.