Income Tax dropped from about 33% (5-6% of GDP) in the early 1950s, to less than 10% (1.3% of GDP) in 2010.
In contrast, payroll taxes provided 40% (6% of GDP) of Fed Govt revenue in 2010, 4-x its 10% share (1.6% of GDP) in the early 1950s.
The individual income tax has consistently provided nearly 50% of total Federal revenue (avg 8% GDP) since 1950.
Individual income taxes and payroll taxes accounted for 82% of all Federal revenues (14% of GDP) in fiscal year 2010.
Corporate income taxes contributed 9% in 2010, down from 33% in 1950."
US-Fed-Govt’s Sources of Revenue/full-data-graghs
/expenses.cfm, Fed-State-Local: /revenue-breakdown.cfm, US-vs-intl: /international.cfm