How long a trademark lasts in the U.S. does depend on declaration and renewal filings. Trademarks are capable of perpetual existence, but must be renewed every ten years. In addition, a declaration between the 5th and 6th anniversary is required, and a declaration plus renewal is necessary during the 9th and 10th anniversary. While there is a 6 month grace period, please keep these dates in mind. This is repeated every decade so long as the trademark is in use.