1. On which.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• wheren,
• whern,
• whereup,
• wherent,
• whren,
• wherea,
• wepeon,
• wherin,
• werson,
• wheree,
• wherehe,
• whereva,
• wheen,
• werein,
• wherer,
• whereyou,
• wherew,
• weren,
• whereit,
• wherewe

• wherein.

The plural form of "whereon" is "whereons".

The singular form of the word "whereon" is "whereon". It is both the singular and plural form of the word.