sauce:
US Census Bureau

release:
County population estimates by race and ethnicity

unit:

Mannot seasonally adjusted

frequency:

yearly

Note:

Data were obtained from ACS Demographic and Housing Estimates, Table DP05.

American Community Survey (ACS) multiyear estimates are derived from data samples collected over a period of time, as opposed to “point-in-time” estimates such as past decennial censuses. This is the estimated value of the “period”. His five-year estimate of ACS includes data collected over 60 months. The data date is the end of his five-year period. For example, a date value of 2014 represents data from 2010 to 2014. However, it does not describe specific days, months, or years within that period.

Multi-year estimates require several considerations that are not necessary for single-year estimates. For example, multi-year estimates published consecutively consist mostly of overlapping years and shared data. The 2010-2014 ACS 5-year estimates share sample data from 2011-2014 with the 2011-2015 ACS 5-year estimates. Because of this overlap, users should use extreme caution when comparing multi-year estimates to consecutive years.

See “Section 3: Understanding and Using ACS Single-Year and Multi-Year Estimates” on page 13 of the publication (page 19 of the file). 2018 ACS General Handbook For a more thorough explanation.