As of 2000, the population is 71,558. The county seat is at Coupeville. Its largest city is Oak Harbor.

Its name reflects the fact that it consists of just two islands, Whidbey and Camano. Island County was created out of Thurston County on January 6, 1853, by the legislature of Oregon Territory, and is the 8th oldest county in Washington. It originally encompassed what are now Snohomish, Skagit, Whatcom County, and San Juan Counties.

Island County is divided in many ways between its north and south. While the north (Oak Harbor) is very conservative and voted for George W. Bush with almost 65 percent of the vote and carrying all precincts, all southern and central precincts voted for John Kerry. The south-central area (Coupeville, Langley) voted over 60 percent for Kerry. Camano Island has a Republican lean and went for Bush with 52 percent of the vote, but is much less polarized than the rest of the county.