Find a valid address for the player you wish to write to. There are a variety of websites on the Internet that claim to have contact information for sports figures and celebrities, but not all of them are legitimate. It is important that you find the correct address. Your best bet is to visit the official Dallas Cowboys website at dallascowboys.com. While the website does not have individual contact information for each player, it does have detailed information on each player and also a contact form in which you can email the team and you may be able to obtain an address that way.
Become a member of a fan club for the Dallas Cowboys. Make sure it is the official fan club of the team, which can be found at truebluefanclub.com. Fan clubs offer memberships which contain certain perks such as autographed photos, invitations to special events where players will be present and contact information. You can also send a letter to the president of the fan club who can pass your letter along to the player.
Use a social network such as Facebook or Twitter. The Dallas Cowboys have an official Facebook page and many of the players have Twitter accounts. By following these types of networks you will often see personal posts from the players and you can also post on their page or send them a "tweet." You may be able to obtain an official address this way in which to send your letter, or an email address. You can also write to them directly on the Facebook page.
Write a letter to the Dallas Cowboys main office in Irving, Texas. While it is not a specific address for an individual player, it is the official office and training center for the team, and mail can be passed to the players this way. The address for the facility is: Cowboys Center One Cowboys Parkway Irving, TX 75063-4727