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Historical Geography & Data Availability
Geographic Areas Reference Manual
Describes in great detail the basic geographic entities the Census Bureau uses in its various data tabulations and documents the purposes, definitions, standards, criteria, and procedures used to select, define, delineate, and revise these geographic entities up to 1990.
Data availability for census tracts by county (1910-1980) [PDF]
Before 1980 not all counties were divided into tracts. In 1990 and 2000 all counties were fully tracted. This lists the tracts as they were created.
Census Geography: General
Census Geography: Specific Geographies
Census Bureau Legal and Statistical Geographic Entities Diagram