The American Goldfinch is the state bird of Washington. It is common throughout the lowlands of Washington, often coming to bird feeders. The male in breeding plumage is bright yellow with a black forehead, wings, and tail. He has one white wing-bar on each wing and white on his tail. Outside of the breeding season, the male is drab brown with hints of yellow and white wing-bars. In both breeding and non-breeding plumage, he has white undertail coverts contrasting with the yellow undertail coverts of the Lesser Goldfinch. The female in breeding plumage is yellowish-gray-brown on top and varies in color from bright yellow to dull yellow underneath. She has two light wing-bars on each wing and a light-colored bill. Her tail is black with white outer tips. Outside of the breeding season, she is gray above and below, and has less distinct wing-bars and a darker bill.

American Goldfinches can generally be found in brushy and weedy habitats at the edges of fields, rivers, and hedgerows, especially when thistle is present. Suburban gardens, poplar plantations, orchards, and other brushy areas with scattered deciduous trees are commonly used.

Flocks are common outside of the breeding season, and American Goldfinches often flock with redpolls and Pine Siskins. They are active foragers, and climb about nimbly when foraging, often hanging from seed-heads and other objects. Like many finches, American Goldfinches have an undulating flight. They often give call notes on the upward strokes

Small seeds, especially thistle, make up the majority of the American Goldfinch's diet. In the summer, they eat some insects, especially aphids, but seeds dominate their diet. They feed regurgitated seeds to their young.

American Goldfinches breed later in the summer than most songbirds. Their breeding is timed to coincide with the peak abundance of thistle seed. They often nest in loose colonies. The nest is located in an upright fork of a shrub, tree, or occasionally a dense weed. The female builds a tightly woven, compact cup of plant fibers and spider webs and lines it with thistle-down. The female incubates 4 to 6 eggs for 12 to 14 days. The male brings her food while she incubates, and while she broods the young for the first few days after they hatch. After that, both parents bring food to the young. The young leave the nest after 12 to 17 days, but the parents continue to feed the young for a few weeks. American Goldfinches generally raise one or two broods each year.