[6] The Swinomish are closely related to their historical neighbors, including the Squinamish,[7] Lower Skagit, and Kikiallus peoples.

In the early colonial period, whites believed that the Swinomish were a part of the Lower Skagit, however, they were separate and distinct peoples.

[8] Around 1830–1835, a major smallpox epidemic blazed through the villages of Skagit County, including the Swinomish.

Their territory included the entire eastern half of Fidalgo Island down to Deception Pass, all of Whidbey Island above the northern half of Dugualla Bay, as well as a portion of Padilla Bay and the mainland north of the Skagit River extending about halfway to what is now Mount Vernon.

[14] Like other Coast Salish peoples, the Swinomish traditionally built permanent villages along waterways, especially near fresh water outlets like rivers and creeks.

[7] One of the main villages of the Swinomish was located near the headwaters of Sullivan Slough, near today's La Conner.

Its strategic value was further amplified by its location: it could only be reached by large war canoes at high tide.

[16] The lifestyle of the Swinomish, like other Indigenous peoples of the Northwest Coast, is highly reliant on the usage of marine resources, such as salmon fishing and shellfish gathering.

They reserved the right to fish and harvest in their usual and accustomed areas in the Point Elliott Treaty of 1855.

Around three-fourths had made the switch, with the remainder still living engaged in traditional subsistence patterns.

A Shaker church was built on the Swinomish Reservation in 1939, but individuals practiced privately in their homes since 1910.

According to their tradition, their language originated with the Kikiallus, from whence the Swinomish and other Skagit-speaking peoples migrated.

[15] In historic times, many also spoke Chinook Jargon, a trade language used for communication between settlers and Indigenous peoples in the 19th century.