FROM the William Hill Website:

Restrictions for US clients:
Pending clarification of the scope and enforceability of the Wire Act and applicability of state and federal laws as regards online gambling by US citizens, William Hill have taken steps to cease accepting casino and poker business from clients with a US address or US issued credit cards.

Such steps are already in place to prevent Internet sports betting by US domiciled individuals.

Existing US clients with funds in their account may only log into their account to withdraw all funds. This can be achieved by following this link – http://www.willhill.com

Once logged into the account simply choose My Account and then Make A Withdrawal.