Neighboring provinces are (from the southwest clockwise) Samut Songkhram, Ratchaburi, Nakhon Pathom, and Bangkok. Samut Sakhon is part of the Bangkok Metropolitan Region.
Samut Sakhon is at the mouth of the Tha Chin River, a distributary of the Chao Phraya River, to the Gulf of Thailand. At the coast are many salt pans used for harvesting sea salt. The total forest area is 42 km² or 4.9 percent of provincial area.