Q. Educational attainment by state?

Education attainment by state

The best sources are the Census and American Community Survey.  However not all years are covered.

For years not covered use the Current Population Survey.  Not all states will be included due to small sample sizes.

The Digest of Education Statistics from the National Center for Education Statistics (NCES) does by year
(latest) https://nces.ed.gov/programs/digest/d22/tables/dt22_104.80.asp?current=yes

Older:  https://nces.ed.gov/pubsearch/getpubcats.asp?sid=091#061 . For data back to 1990, also try the Digest's online List of Tables and Figures

For national data by various characteristics back to 1940, see the Census Bureau site.

Also see FRED.