Siam is an unincorporated community in Reed Township, Seneca County, Ohio, United States.

It is located along State Route 4, just north of Attica.

The community is served by the Attica (44807) post office.

[2] Siam was originally called Detroit; under the latter name had its start in 1875 when the railroad was extended to that point.

This Seneca County, Ohio state location article is a stub.