In Federal Register Vol. 75, No. 123 published on Monday, June 28, 2010, the Office of Management and Budget outlined a process by which core based statistical area boundaries would be updated five-years after the delineations from the 2010 Census were published in 2018.

On September 14, 2018, OMB Bulletin No 18-04 published the planned revisions to Metropolitan Statistical Areas, Micropolitan Statistical Areas, and Combined Statistical Areas and published guidance on uses of those area.

Delineations of the revised areas was completed using the 2018 TIGER Line data from the US Census Bureau and List 1 from the OMB bulletin. Data from List 1 was published in excel format to the Census Bureau’s website in September 2018. The data were joined and new metropolitan/micropolitan areas and combined statistical areas were generated.

For more info see:

• Federal Register: https://www.govinfo.gov/content/pkg/FR-2010-06-28/pdf/2010-15605.pdf

• OMB Bulletin: https://www.whitehouse.gov/wp-content/uploads/2018/09/Bulletin-18-04.pdf

• Census Delineation files: https://www.census.gov/geographies/reference-files/time-series/demo/metro-micro/delineation-files.html