You can report cash income under 'Miscellaneous' income which can be found under 'Less Common Income'. You will see 'Other income not already reported on a Form W-2 or Form 1099' under the miscellaneous category. This section is for:
- Wages earned as a household employee not reported on Form W-2
- Sick or disability pay not reported on Form 1099-R
- Excess salary deferrals
- Community property earned income adjustments
- Other wages received not reported elsewhere
If the income is from Self-Employment, your enter it under the "Self-Employment Income and Expenses" section and TurboTax will walk you through setting up your Schedule C.
Here is some IRS info to help you determine if your income is from self-employment: Who is Self-Employed?