Lists major releases of historical census data online for the country, states, cities, metro areas, etc. Very useful starting point for historical census questions.

Instructions given to census takers from 1850-2000. It's important to note that census takers filled out the forms until 1960, when self-enumeration began in part.

The following reports are published from the 2002 Economic Census, Company Statistics (CS)
Series, Survey of Business Owners, and include totals for all U.S. businesses based on the 2002
Economic Census and estimates of business ownership by gender, Hispanic or Latino origin, and
race based on the 2002 SBO. Estimates for equally male-/female-owned firms and publicly held
companies and other businesses whose ownership cannot be classified by gender, Hispanic or
Latino origin, and race are tabulated and published separately.

Information on educational attainment of the U.S. population has been collected in every decennial census since 1940.  In 1940, educational attainment was collected for every person enumerated in the census (i.e., 100% data) and on a sample basis thereafter.  At the national level, this report includes tables that show rates of educational attainment by age, sex, race, and Hispanic origin.  At the regional and state levels, educational attainment data are shown by sex, race, and Hispanic origin.  The tables show two attainment levels:  the percent of the population 25 years and over with a high school diploma or more education and the percent with a bachelor’s degree or more.