About January 1, 1806, a group of men from the Lewis and Clark Expedition built a salt-making cairn at the site later developed as Seaside. The city was not incorporated until February 17, 1899, when coastal resort areas were being settled. It is about 79 miles by car northwest of Portland, Oregon, a major population center.
In 1912, Alexandre Gilbert (1843–1932) was elected Mayor of Seaside. Gilbert was a French immigrant, a veteran of the Franco Prussian War (1870-1871). After living in San Francisco, California and Astoria, Oregon, Gilbert moved to Seaside where he had a beach cottage (built in 1885). Gilbert was a real estate developer who donated land to the City of Seaside for its one-and-a-half-mile-long Promenade, or "Prom," along the Pacific beach.
In 1892 he added to his beach cottage. Nearly 100 years later, what was known as the Gilbert House was operated commercially as the Gilbert Inn since the mid-1980s. Both it and Gilbert's eponymous "Gilbert Block" office building on Broadway still survive.
Seaside lies on the edge of the Pacific Ocean, at the southern end of the Clatsop Plains, about 29 km (18 mi) south of where the Columbia River empties into the Pacific. The city is developed on both sides of the Necanicum River, which flows to the ocean at the city's northern edge. Tillamook Head towers over the southern edge of the city.