If you have one account: You'll find the account number in the upper right corner of page one of the statement. 

If you have more than one account: We'll send a one statement with the details of each account.

• The primary account number is in the upper right corner of each page.
• All other account numbers are to the right of the name of the account.

See also: Why did I get one statement when I have multiple accounts with U.S. Bank?