Census Bureau Releases Vintage 2024 State Population Estimates
On December 19th, 2024, the U.S. Census Bureau released their Vintage 2024 population estimates for the nation and states. This estimates series incorporates a methodological change to how the Census Bureau estimated net international migration, resulting in substantially higher nationwide estimates of net international migration over the last several years. This change was implemented at the national level and the resulting increase in net international migration was distributed to states based on estimates from the American Community Survey. However, the Census Bureau is currently researching the best way to distribute this nationwide international migration adjustment to states and counties. Therefore, it is likely that states’ international migration estimates for these years will be revised again when the next annual vintage of estimates is released.
In this blog post, we will discuss:
How Connecticut’s population estimate changed
What drove this change in Connecticut’s population estimate
Why and how the Census Bureau changed their methodology for estimating net international migration
How Did Connecticut’s Population Change?
The newly-released estimates show Connecticut’s total population increasing by 32,046 residents (+0.88%) between July 1, 2023, and July 1, 2024. The most recent vintage also revised Connecticut’s total population estimate upward by 25,847 residents (+0.7%) for July 1, 2023, and by 9,219 residents (+0.3%) for July 1, 2022, compared to the estimates for those years in the prior vintage.
In total, the 2024 population estimate shows an increase of 57,893 residents (+1.6%) compared to Connecticut’s 2023 total population estimate from Vintage 2023.
What Drove the Change in Connecticut’s Population?
The Census Bureau estimates total population change at the national, state, and county levels by adding components of change to the population count as of the last decennial census (April 1, 2020). These components of change consist of natural change (births minus deaths), net domestic migration, and net international migration. The charts below show the total population change and components of change across each time point in the Vintage 2023 and Vintage 2024 estimates series.
When comparing the components of change in Vintage 2024 to those in Vintage 2023, it is clear that the higher estimates of Connecticut’s total population in 2022 and 2023 from Vintage 2024 are due primarily to a large increase in the net international migration component in the most recent vintage.
Compared to Vintage 2023, the Vintage 2024 estimates of net international migration for Connecticut were greater by 6,793 (+44%) in 2021-2022 and by 14,704 (+96%) in 2022-2023.
Net domestic migration was also less negative by 2,554 (28%) for 2022-2023 in the Vintage 2024 estimates. This, combined with the large increase in net international migration estimates, further increased the difference between vintages in the 2023 population estimate.
In contrast, the Vintage 2024 estimates of natural change were nearly identical to those from Vintage 2023 for all overlapping years.
It is also clear that Connecticut’s estimated population increase of 32,046 residents between 2023 and 2024 is due almost entirely to international migration.
The Vintage 2024 estimates suggest that Connecticut gained 36,214 in net international migration between 2023 and 2024.
In that same time period, the Vintage 2024 estimates suggest that Connecticut had a net loss of 6,060 in domestic migration and a net natural change of 1,831 (births minus deaths).
Connecticut’s large population growth due to international migration mirrors the Census Bureau’s national population estimates, which showed that net international migration accounted for 84% of the nation’s growth of 3.3 million residents between 2023 and 2024, which was the largest annual national growth rate since 2001. Indeed, as mentioned above, the large increase in Connecticut’s international migration statistics is due to an adjustment in how the Census Bureau estimated net international migration at the national level.
Why and How did the Census Bureau Change their Methodology for Estimating Net International Migration?
Typically, the Census Bureau has estimated foreign-born immigration using American Community Survey (ACS) estimates of the population who resided abroad one year ago. However, as described in a Census Bureau blog detailing the change in methodology, this approach has two important limitations:
(1) The most recent ACS estimates that are available when the Census Bureau is producing their population estimates are at least one year old. As a result, these estimates do not capture short-term fluctuations in international migration, such as those seen during the COVID-19 pandemic or that occur due to changes in immigration policy.
(2) Research suggests that some foreign-born populations are underrepresented in the ACS.
The Census Bureau also maintains a Benchmark Database of federal administrative data on immigration to serve as an independent point of reference. These administrative data revealed a substantial increase over the past few years in the number of humanitarian immigrants to the U.S. (e.g., refugees and asylum-seekers). Furthermore, Census Bureau research suggested that these humanitarian migrants were the least likely to be included in the ACS sample.
Based on analyses of the ACS coverage error and consultation with experts, the Census Bureau adjusted the national foreign-born immigration estimates from the ACS upward to account for 75% of the humanitarian migrants in the Benchmark Database. The results of this adjustment at the national level are illustrated in the figure below, from the Census Bureau’s blog on this topic.
Gross, Mark; Lamas, Jacqueline; Mayol-Garcia, Y. H., & Jensen, E. (December 19th, 2024). “Census Bureau Improves Methodology to Better Reflect Increase in Net International Migration.” U.S. Census Bureau.
The Census Bureau’s Benchmark Database showed steep increases in the number of humanitarian migrants to the U.S. in 2022, 2023, and 2024, which were not being captured by the estimates of foreign-born immigration from the prior year’s ACS data (solid blue line). In the figure above, the dashed blue line illustrates the nationwide adjusted foreign-born immigration estimate (adding on 75% of humanitarian migrants from the Benchmark Database) that was used in the Vintage 2024 population estimates, bringing the net international migration estimate more closely in line with the administrative data. This graph also illustrates the effect of a downward adjustment of the foreign-born immigration estimate that was implemented for July 2020 - 2021 to capture the impact of the COVID-19 pandemic.
For more details on the methodological changes made and the rationale for these changes, see the Census Bureau’s blog: “Census Bureau Improves Methodology to Better Reflect Increase in Net International Migration.”
Limitations of the Census Bureau’s Approach
The Census Bureau is researching ways to improve upon their approach for distributing the nationwide net international migration adjustment to states. For Vintage 2024, they distributed this adjustment to states using their usual method based on ACS estimates of the international migrant population. However, since this adjustment was made to account for the under-sampling of humanitarian migrants in the ACS, this approach likely does not accurately reflect the distribution of these humanitarian migrants across states. The Census Bureau is planning to refine their methodology for distributing this net international migration adjustment in the next population estimates vintage, meaning that state-level population estimates for the past three years are likely to shift again in Vintage 2025.
For More Information
For more information about the Vintage 2024 population estimates, see the Census Bureau’s blog posts Census Bureau Improves Methodology to Better Reflect Increase in Net International Migration and Net International Migration Drives Highest U.S. Population Growth in Decades, and the Vintage 2024 Population Estimates Methodology Statement. You may also be interested in this Census Bureau Working Paper comparing the Census Bureau’s methodology for estimating international migration to that of other federal agencies.
For CTData’s explanations of methodological changes in the population estimates and their impact on Connecticut, see: Understanding the Census Bureau’s Vintage 2023 Population Estimates for Connecticut, The Population Estimates "Blended Base:" What it is and Why it Matters, and Known Errors in the Census Bureau’s Vintage 2022 Population Estimates: Guidance for Data Users.
Visit our population estimates dashboard to explore estimates of Connecticut’s total population at the state, planning region, and town levels; components of population change; and new housing units permitted annually in each town. The newly-released Vintage 2024 state estimates will be added to this dashboard in early 2025.
To learn more about the Census and resources provided by CTData, head to our Census Data portal, where you can learn about the different sources of population data on our Population Statistics Hub and access Census Tools and Resources for your census data project. Explore other data sets and analysis at data by topic and data projects. You can stay up-to-date on the latest data and tools by subscribing to our newsletter and following CTData on Facebook, Instagram, and LinkedIn.