Personal income. Income received by persons from all sources. It includes income received from participation in production as well as from government and business transfer payments. It is the sum of compensation of employees (received), supplements to wages and salaries, proprietors' income with inventory valuation adjustment (IVA) and capital consumption adjustment (CCAdj), rental income of persons with CCAdj, personal income receipts on assets, and personal current transfer receipts, less contributions for government social insurance.
And supplements to wages and salaries is: Supplements to wages and salaries. Consists of employer contributions for employee pension and insurance funds and employer contributions for government social insurance.
And Employer contributions for employee pension and insurance funds: Contributions consisting of employer payments (including payments-in-kind) to private pension and profit-sharing plans, publicly administered government employee retirement plans, private group health and life insurance plans, privately administered workers’ compensation plans, and supplemental unemployment benefit plans, formerly called “other labor income.”
So if 401Ks count as 'private pension plans' then they are included?