Samut Prakan Province is at the far end of the Chao Phraya River, where it empties out into the Gulf of Thailand. The borders to the north and west join the Metropolitan of Bangkok. To the south is the sea and the east Chachoeng Sao Province. Samut Prakan was built between 1620-1628 in the Ayuttaya era. The original site for the city was on the west side of the river at Phra Pradaeng. In 1819, King Rama II commanded to have Samut Prakan re-located across the river at the small fishing village of Paknam. At the same time he built forts along both sides of the river in order to defend the approach to Bangkok. Today, the city is still commonly known as Paknam despite the change of name and status 180 years ago. The name of the city can also be spelled like Samutprakan, Samut Prakarn and Samutprakarn.

Samut Prakan is administratively divided into 5 districts (Amphoes) and 1 subdistrict (King Amphoe): Amphoe Muang Samut Prakan, Amphoe Phra Pradaeng, Amphoe Bang Bo, Amphoe Phra Samut Chedi and King Amphoe Bang Sao Thong.