Snohomish was founded around 1858 by Emory C. Ferguson, E. F. Cady and others. It was originally known as Cadyville, but changed its name to Snohomish City in 1871. The name Snohomish comes from the name of the dominant local Native American tribe, whose meaning is widely disputed. One of the first inland cities in the Puget Sound region, Snohomish was built where a planned military road connecting Fort Steilacoom and Fort Bellingham was set to cross the Snohomish River. The road, proposed in the wake of the Pig War, was intended to be built far enough inland to be safe from British naval attacks. Although the road was never completed, Snohomish quickly became a center of commerce in the expanding region.

In 1861, Snohomish County separated from Island County and the Village of Snohomish was voted the county seat. It remained so until 1897 when the county seat was relocated to the larger, yet much newer neighboring city of Everett, Washington after a controversial and contested county-wide vote.
https://en.wikipedia.org/wiki/Snohomish,_Washington