Westchester County's history can be traced back to the founding of a settlement between Long Island Sound and the Hudson River in the 17th century. The Algonquian-speaking Wappinger Indians, the original inhabitants of Westchester County, named themselves Lenape, which means the people.

Giovanni da Verrazzano and Henry Hudson were the first European explorers to visit the Westchester area. Westchester became one of the original twelve counties of the Province of New York after the surrender of New Netherland to the English in 1664. In 1683, the area was established as one of New York's original counties.

Life in Westchester was relatively primitive during the colonial period. Transportation was heavily dependent on water as the roads were few and in poor conditions. The settlers grew or raised almost everything they consumed on their farm, and for things they couldn't grow, they got by bartering their cattle, woods, and foods.

The area started improving when cottage industries, like shoe and furniture making, sprang up, which led to frequent use of local roads. Ferries were launched, and taverns catering to travelers were established. Westchester became the wealthiest and most populous county in the colony of New York by 1775. Roadways were installed along with the construction of the Tappan Zee Bridge, which led to further growth in the county.

Westchester was named in honor of the city of Chester in England.