Citizens returning to the U.S have no limit on the amount of money they can bring into the country. If the currency totals $10,000 or more, however, you must declare it with U.S. Customs and Border Protection. The CBP requires certain forms from travelers who declare currency. Failure to properly declare the currency could result in civil penalties, criminal prosecution and/or seizure of the money.
All travelers declaring anything with U.S. customs must fill out Form 6059B upon entering the country. If you will be declaring $10,000 or more in U.S. currency, its foreign equivalent or any combination thereof, you must also fill out Form FinCEN 105, the "Report of International Transportation of Currency and Monetary Instruments." You can download Form FinCEN 105 from the U.S. Customs and Border Protection website or obtain one when going through customs while in transit.
Families Traveling Together
The declaration of monies totaling $10,000 or more to the CBP applies to families traveling together, as well as individuals. For instance, if you're traveling with your spouse and you each have $6,000, it's considered $12,000 and must be declared on one FinCEN 105 form.