The 2010 tribal block group concept and criteria are completely different from those used in 2000. For the Census 2000, tribal block groups were the standard state-county-census tract-block group areas retabulated under an American Indian area hierarchy; that is, American Indian area-tribal census tracttribal block group. Tribal block groups only were applicable to legal federally recognized American Indian reservation and off-reservation trust land areas. Tribal block groups were defined to provide statistically significant sample data for small areas within American Indian areas, particularly those American Indian areas that crossed state or county boundaries where these boundaries were not meaningful for statistical purposes. The 2000 tribal block groups used the block group numbers and comprised all blocks beginning with a single number.
The 2010 tribal block groups are defined independently of the standard county-based block group delineation. For federally recognized American Indian tribes with reservations or off-reservation trust land and a population less than 1,200, a single tribal block group is defined. Tribal participants in qualifying areas with a population greater than 1,200 could define additional block groups within their reservation and/or off-reservation trust land without regard to the standard block group configuration.
Tribal block groups will contain blocks beginning with the same number as the standard county-based block group and could contain seemingly duplicate block numbers. To better identify and differentiate tribal block groups from county-based block groups, tribal block groups use the letter range A through K (except "I," which could be confused with a number "1") to identify and code the tribal block group. Tribal block groups nest within tribal census tract.