Crosswalk files for County Subdivisions between 2010 and 2020

I am working on a project in which I would like to compare the total population at the county subdivision level from 2011 to 2020.
There is a relationship file available on the Census website but I could not find any equivalents here on NHGIS.
I also considered using the block group crosswalk files and re-calculating the total population from the block group level. But I still cannot find the full list of block groups under the county subdivisions.
Could anyone give me any idea and help me on that? Thanks!

Hi Yanmin,

There’s no consistent relationship between block groups and county subdivisions, however, you can calculate populations for subdivisions using blocks. Decennial census data is available on the block level, crosswalks for which you can find on the NHGIS geographic crosswalks page. Each record in the crosswalk identifies a possible intersection between a single source block and a single target block and includes interpolation weights which estimate the proportion of the source zone’s population located in the target zone. You can follow the provided instructions on using block crosswalks to generate data for larger areas, like county subdivisions.

Alternatively, you can find time series data on the county subdivision level using the NHGIS Data Finder tool. Population tables are available both using nominal integration, allowing for study of changes in characteristics of county subdivisions according to their legal definitions, and tables where county subdivisions are standardized to their 2010 versions.

Thank you so much for your explanation!