On a Federal level, so far anyway, if it's not posted to a W-2 or a 1099 (maybe some other reporting forms I'm not aware of), or as part of a licensed business transaction, the IRS isn't going to pick it up as income unless you choose to raise a flag about it. While the $10k number is a flag, as stated above, the banks will also report smaller transactions if there's a pattern of "frequent" deposits...........primarily looking for drug transactions, money laundering, that sort of thing. That doesn't automatically mean that the IRS will nail you for undisclosed income, but you could invite scrutiny from them as well as the FBI, DEA, Homeland Security, and who knows how many other busy body agencies.