Where Did Connecticut Go? A Tale of Belated Geographic Boundary Changes

Census tract boundaries only change with the decennial census. That’s how it works, and why NaNDA provides datasets using multiple geographic boundaries. Except when the Census Bureau decides, in 2022, to finally reflect Connecticut’s 1960 governmental restructuring.

Researchers merging NaNDA Tract20 datasets with data collected in 2022 or later may have noticed Connecticut census tracts missing or mismatched.

What Happened

In 2022, the U.S. Census Bureau adopted Connecticut’s nine Councils of Governments (COGs) as county equivalents, replacing the state’s eight counties for statistical purposes. Connecticut’s counties ceased functioning as governmental entities in 1960; the COGs, which also serve as Planning Regions, carry out the administrative functions typically performed by counties in other states. This change created new FIPS codes for all 879 Connecticut census tracts—a rare mid-decade boundary update. Census Bureau data products transitioned to using these county equivalents throughout 2023-2024.

Why It Matters for NaNDA Users

Many NaNDA datasets use 2020 census geography. When merging NaNDA Tract20 data with data collected in 2022 or later, Connecticut tracts won’t have matching FIPS codes—so they’ll drop out of the merge entirely. The result: Connecticut disappears from the analysis.

The Solution

For existing Tract20 NaNDA datasets that don’t yet include Connecticut’s 2022 FIPS codes, a crosswalk is available in the ICPSR Linkage Library.

This deposit includes:

• A crosswalk between Connecticut 2020 and 2022 tract FIPS codes
• Stata code for applying the crosswalk to NaNDA datasets
• Files in multiple formats (CSV, Stata, Excel)

The code adds a tract_fips22 variable to the dataset. For analyses using 2022 or later data that include Connecticut, use tract_fips22 instead of tract_fips20. 

These files are also accessible on NaNDA’s GitHub.The original crosswalk was created by CT Data Collaborative. 

Note: Future NaNDA data releases will include tract_fips22 as a standard variable in Tract20 datasets.

Questions? Contact us at [email protected] or sign up for NaNDA’s Virtual Office Hours