Devil's Lake State Park is a state park located in the Baraboo Range in eastern Sauk County, Wisconsin, United States. It is just south of the city of Baraboo, around 35 mi (56 km) northwest of Madison, and is on the western edge of the last ice-sheet deposited during the Wisconsin glaciation. The state park encompasses 9,217 acres (3,730 ha); it is the largest state park in Wisconsin. The state park is known for its 500-foot-high (150 m) quartzite bluffs along the 360-acre (150 ha) Devil's Lake, which was created by a glacier depositing terminal moraines that plugged the north and south ends of the gap in the bluffs during the last ice age approximately 12,000 years ago. The sand at the bottom of Devil's Lake is thought to be deposited by glaciers.

There are many quartzite rock formations, such as Balanced Rock and Devil's Doorway, throughout the park. Effigy mounds are also located throughout the park. The park contains approximately eleven miles of the 1,200-mile (1,900 km) Ice Age Trail. It is consistently ranked as the most visited Wisconsin state park. During the fall, the park's brilliant foliage makes it a popular attraction. Parfrey's Glen, Wisconsin's first state natural area, is managed by Devil's Lake State Park and located just east of the park.

The original inhabitants of the area around the lake date back much further than when the European settlers first discovered the land. There is proof that humans occupied the land between 12,000 and 16,000 years ago, but Ho-Chunk historians speak of people living there longer than 300,000 years ago. The area may have been inhabited originally between 12,000 and 16,000 years ago due to the fact that this was the time the last of the glaciers had receded from the area. Many Native tribes throughout Wisconsin inhabited the lands. They called the lake various different names, such as Tewakakak or Minnewaukan, which translate to spirit lake in various Native American Languages.

The area where the park now stands was first settled by pioneers in the mid-1800s. By the start of the 20th century, the area had become a popular vacation destination for wealthy families from Chicago and Madison. The first hotel was established in 1866, 50 years before the park was founded.

The park was founded in 1911. It was home to five resorts, two of which were perched on the west bluff. Few traces of these structures remain, though footings and foundational structures can be found along the South shore and near Prospect Point on the West Bluff. There were also many private residences in the west and south shores of the lake, only four of which remain. At various times the lakeshore hosted water slides, lodges, ferry boat launches and golf courses. The clubhouse of one course sat on the current location of the park's nature center. By the 1940s, the hotels were all closed, and the park was retreating to its former natural self.

From 1934 to 1941, approximately two hundred members of the Civilian Conservation Corps resided in a work camp. These young men, led by Alonzo W. Pond, built many of the trails, buildings, and benches still in use today.

In 1974, the National Park Service declared the Southern portion of the Baraboo Hills a National Natural Landmark. The Nature Conservancy also designated it as one of the "Last Great Places," one of only 77 such designations in the world.

In 2020, a man was stabbed to death along the Grottos Trail. Several witnesses reported seeing a man running from the scene of the murder, but he remains unidentified. As of 2024, the case remains unsolved.