ACS estimates use the legal boundaries as defined and available effective January 1^st of the estimated year. For 3- and 5-Year estimates, the boundaries that are available and effective as of January 1 of the last year of the multiyear estimate period are used. So, for example, the 2005-2009 ACS 5-year estimates are based on boundaries as of January 1, 2009 which is the 2000 Census. Whereas the 2006-2010 ACS 2010 5-year estimates will be based upon the new 2010 boundaries.

If you want the data in the 2000 boundaries – select the 2009 ACS. If you want the data in the 2010 boundaries than select the 2010 (or later) versions instead.

The ACS includes Data for the following geographies (the number in brackets indicates how many of each geography exist in the US including Puerto Rico)

• US (1)
• Region (4)
• Division (9)
• State (52 includes Puerto Rico and Washington DC)
• County (3,221)
• County Subdivisions (36,642)
• Place (29,514)
• Census Tract (74,002)
• Block Group (220,334)
• Consolidated City (7)
• American Indian Area/Alaskan Native Area/Hawaiian Home Land (720)
• Alaska Native Regional Corporation (12)
• Metropolitan and Micropolitan Statistical Area (1,026)
• Combined Statistical Areas (163)
• Metropolitan Statistical Areas – Micropolitan Division (29)
• Metropolitan / Micropolitan Indicator Flag (29) – not mapable just data
• New England City and Town Areas (52)
• New England City and Town Combined Statistical Areas (17)
• New England City and Town Area Divisions (9)
• Urban Areas (3,607)
• Current Congressional District (437)
• State Legislative District Upper (1,976)
• State Legislative District Lower (4,786)
• State School District (Elementary) (2,328)
• State School District (Secondary) (533)
• State School District (Unified) (10,916)
• Urban/Rural (104) – not mapable just data
• Principal City Indicator (1,309) – not mapable just data
• Public Use Microdata 5% file (2,101)