He also had a daughter, Martha J Downey (b. 28 Jun 1856), that married James Madison Riley.
Note: There is some disagreement about whether his middle name is Walter or Seward. The death certificate has a W but the informant was a son-in-law who didn't even know William's parents' names. There is also conflicting information on his birth state. The DC says North Carolina, but all census records say either Indiana or Kentucky. If you have any records to clear any of this up, please send it my way.