Block Group (BG)

Overview

Block Group (BG) is a geographic unit used by the U.S. Census Bureau that is a subdivision of a census tract and typically contains between 600 and 3,000 people. Block groups are the smallest geographic unit for which the Census Bureau publishes sample data from the American Community Survey (ACS).

Key Concepts

Census block is the smallest geographic unit, bounded by visible features; block groups contain multiple blocks. Census tract is the parent geography containing one or more block groups. GEOID is the unique identifier formatted as: STATE(2) + COUNTY(3) + TRACT(6) + BLOCK GROUP(1). ACS data is American Community Survey data available at the block group level. Population threshold is the target of 600-3,000 people per block group.

Geographic Hierarchy

State
└── County
    └── Census Tract
        └── Block Group (1-9 per tract)
            └── Census Block (many per BG)

Data Availability

Survey	Block Group Data
Decennial Census	Full count (100%)
American Community Survey	Sample estimates with margins of error
Economic Census	Limited

Appendix

Created: 2025-12-13 | Modified: 2025-12-13

See Also

• Federal Information Processing Standards (FIPS)
• Census Tabulation Block (TABBLOCK)
• Topologically Integrated Geographic Encoding and Referencing (TIGER)
• US Census Bureau

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