Sandusky (/sænˈdʌski/ san-DUSS-kee) is a city in Erie County, Ohio, United States, and its county seat. Situated on the southern shore of Lake Erie, Sandusky is located roughly midway between Toledo (45 miles (72 km) west) and Cleveland (50 miles (80 km) east). At the 2020 census, the city had a population of 25,095, and the Sandusky metropolitan area had 115,986 residents.

Sandusky was established in the early 19th century and developed as a port city at the head of Sandusky Bay. It is home to Cedar Point, one of the most popular amusement parks in the world, as well as water parks including Cedar Point Shores, Castaway Bay, Great Wolf Lodge, and Kalahari. The headquarters of Cedar Fair Entertainment Company were located in the city until it merged with Six Flags, who retains some administrative offices in Sandusky.

The accepted etymology is that the name "Sandusky" is derived from the Wyandot word saundustee, meaning "water" or andusti, "cold water". In his 1734 history of New France, Charlevoix transliterated the word as "Chinouski". Sandusky Bay, formed at the mouth of the Sandusky River, is identified as "Lac (Lake) Sandouské" on a 1718 map by Guillaume DeLisle. The name "L.(Lac) Sandoski" appears on a 1733 map. Sandusky Bay was also called Lac Ondaské, in another French transliteration of the Wyandot.

The river and bay gave rise to a number of eponymous forts and settlements along their shores. These consisted of the short-lived English trading post Fort Sandusky north of the bay, the French Fort Sandoské that replaced it, the British Fort Sandusky on the south shore of the bay, the American Fort Sandusky (later Fort Stephenson) upriver at Lower Sandusky (now known as Fremont, Ohio), as well as the Wyandot Indian village of Upper Sandusky farther upriver.

Another, less accepted etymologic version claims that the city's name goes back to a Polish–American trader and frontiersman named Anthony Sadowski, a neighbor of the Boone family and co-founder of Amity village. He was employed by the governor of then British Pennsylvania as a trader and interpreter, speaking several Indian languages, especially Iroquois. He moved to the Pennsylvania frontier in January 1712 and could easily have made it to Lake Erie by 1718 to establish a trading post. One genealogical line of his descendants is actually called "Sandusky".^{[citation needed]}

This area was a center of trading and fortifications since the 18th century: the English, French, and Americans had trading posts and forts built on both the north and south sides of Sandusky Bay.

George Croghan was one of the more prominent men who operated in this area in the 18th century. A federal fur trade factory was established in 1808 but was lost at the beginning of the War of 1812.

Development by European Americans of the city of Sandusky, starting in 1818, on the southeast shore of Sandusky Bay, followed settlement of the war of 1812. Part of the city quickly enveloped the site of an earlier small village named Portland (established about 1816). Sandusky was incorporated as a city in 1824. Eventually the city of Sandusky encompassed most of the entire township that had been called Portland. Some of the city was built on land formerly occupied by a Native American man named Ogontz, and therefore the city is said to have been built on "Ogontz' place".