Source: U.S. Census Bureau
Release: Educational Attainment
Estimate of educational attainment for population 18 years old and over whose highest degree was a bachelor's, master's, or professional or doctorate degree. (ACS variable S1501_C02_015E from table S1501.)
For more information about the subject definitions, see: https://www.census.gov/programs-surveys/acs/technical-documentation/code-lists.html.
Single-year estimates from the American Community Survey (ACS) are "period" estimates derived from a data sample collected over a period of time, as opposed to "point-in-time" estimates such as those from past decennial censuses. ACS single-year estimates include data collected over a 12-month period; explicitly the calendar year (e.g., the 2015 ACS covers the period from January 2015 through December 2015).
Please see the ACS handbook (Section 3, "Understanding and Using ACS Single-Year and Multiyear Estimates" p. 13) for a comprehensive set of details and clarifications: https://www.census.gov/content/dam/Census/library/publications/2018/acs/acs_general_handbook_2018.pdf"
U.S. Census Bureau, Bachelor's Degree or Higher for Illinois [GCT1502IL], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/GCT1502IL, August 18, 2019.