William Yenson was born in Kingston Bagpuize in 1880. He joined West Ham United in 1902. He played only five league games in his first season. The following season Yenson he was a regular in the side until he was sold to Bolton Wanderers. Yenson appeared in the 1904 FA Cup Final against Manchester City, a game they lost 1-0.

Yenson scored 8 goals in 28 games before joining Queen's Park Rangers. He returned to West Ham United in 1908 and joined a team that included Herbert Ashton, Jack Foster, Tommy Allison, Fred Blackburn, George Chalkley, Billy Grassam, Alfred Harwood, Len Jarvis, George Kitchen, Frank Piercy, Tommy Randall, Danny Shea, George Webb and Robert Young. Yenson played in 32 cup and league games that season.

In 1909 Yenson joined Croydon Common where he scored two goals in 36 games.