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What happens if you deposit more than $10,000 in cash?
Short answer
In the US, the bank files a Currency Transaction Report (CTR) with FinCEN for any cash deposit or withdrawal over $10,000 in a day. It's automatic and routine. Filing one doesn't mean you did anything wrong.
The report includes who made the transaction, their ID and the amount. Several cash transactions by the same person on the same business day count together.
Most people who trigger a CTR are businesses that handle a lot of cash. The trouble starts when someone tries to avoid the report.
Sources: 31 CFR § 1010.311 (eCFR) · FinCEN
US federal rules, explained for a story. Not legal advice.