[3] Patches of woodland are all that remain of the brush and light forest that once covered the county.

In ancient times, the woodlands contained a great deal of timber, but Native Americans burned them periodically to encourage the growth of berries.

French fur traders were the first Europeans to enter this land, traveling by river across the county.

At the mouth of the Trempealeau River at its confluence with the Mississippi River, they found a bluff surrounded by water and called it La Montagne qui trempe à l’eau ("mountain steeped in water").

[9] During the 19th and 20th century large numbers of Norwegian immigrants settled in the area in pursuit of cheap land, a better life and more opportunities.

[citation needed] In the late 1850s, Trempealeau became a destination for Polish Prussian settlers from Upper Silesia seeking to escape German persecution and poverty in their homeland.

They built churches, schools, and communities to develop what became the nation's second-largest Polish settlement.

The county again became an immigrant destination in the first decades of the 21st century, gaining a significant Hispanic and Latino population.

Then, from 1988 to 2012, like most of the rural counties in southwestern Wisconsin, it backed the Democratic candidate in each election, and did so by more than a 10% margin each time.