When part of the New Netherland colony, Dutch traders first called the area of present-day Ulster County "Esopus", a name borrowed for convenience from a locality on the opposite side of the Hudson.

In 1683, the Duke of York created 12 counties in his province, one of which was Ulster County, named after Prince James, Duke of York (later King James II of England) whose subsidiary titles included Earl of Ulster.

The official records of Ulster County were removed to safety to a stone house in Kerhonkson when it became evident that the British would burn Kingston.

[A] During the American Civil War, volunteers were recruited from the county and formed the majority of the following regiments: Other regiments with at least one company from the county included: The Lake Mohonk Mountain House on Shawangunk Ridge was designated a National Historic Landmark in 1986.

[7] Ulster County is in southeastern New York State, south of Albany, immediately west of the Hudson River.

The Sam's Point section of Minnewaska includes rare dwarf pine trees and Verkeerder Kill falls.

11.61% of the population were Hispanic or Latino of any race For most of the 20th century, Ulster County voted for the Republican nominees for president.

Republicans regularly got over 60% of the vote, the high point coming when Dwight D. Eisenhower won 76% in 1956.

The Democratic nominee won only in 1912, when Theodore Roosevelt and his Progressive Party split the Republican vote and gave a plurality to Woodrow Wilson, and in 1964, when Lyndon B. Johnson won every county in New York and carried Ulster County by 19.8 percentage points.

The more populated eastern half of the county is in New York's 18th congressional district, represented by Democrat Pat Ryan.

The less populated western half of the county is in New York's 19th congressional district, represented by Democrat Josh Riley.

Ulster County had no U.S. representative after Antonio Delgado resigned on May 25, 2022, to become lieutenant governor of New York.

Ryan won a special election on August 23 against Marc Molinaro, and was sworn in on September 13.

In 2006, voters approved the first-ever county charter, changing to an elected executive branch.

[15] In early 2019, Hein resigned to accept Governor Andrew Cuomo's appointment as commissioner of the state Office of Temporary and Disability Assistance.

[19] Democrat Jen Metzger, a former New York State Senator, defeated Republican Jim Quigley in the 2022 election to replace Ryan.

Former Orleans band member John Hall served in the Ulster County legislature before moving to the 19th Congressional District to run for Congress.

Each offers various recreation opportunities, including hiking, bicycling, skiing, horseback riding, kayaking, rock climbing, hunting and fishing.

[23] Also since 2015, the Saugerties Stallions, a collegiate summer baseball league team that plays in the Perfect Game Collegiate Baseball League (PGCBL), have been based in Saugerties and play their home games at Cantine Field.