On the 1851 census, William is unmarried.
1841 census does not show Condition, so how do you know he was married?!

Oh! And he was born in Il
chester, not Ilminster?
Reference HO107, Piece 1930, Folio 515, Page 20
Market Place, Ilchester
Francis, William Head Unmarried M 42 LWSA Lond MRCS Lond In General Practice b Ilchester
Pitman, Ann Servant F 46
Miller, John Servant M 15
1841 census says:
Reference HO107, 960, 1/9, 11
Church Street, Ilchester
Francis, William M 30 Surgeon
Francis, Eleanor F 20 Not born in County
Francis, Eleanor F 1 Foreign
Francis, unknown F 2 days
Rapson, Jane F 20 F.S. (Female Servant)
Sibley, Sarah F 15 F.S.
Noble, James M 19 Apprentice Surgeon
Taylor, Sarah F 50 F.S. all born in county, except where shown
Eleanor could be his sister? cousin?