Last Green Valley National Heritage Corridor

The Old Killingly High School is a historic school building on 185 Broad Street in the Danielson section of Killingly, Connecticut. Built in 1908 and enlarged in 1927, it served as the town's high school until 1965, and then its junior high school until 1990. It is a significant local example of Renaissance and Colonial Revival architecture, designed by Hartwell, Richardson & Driver. It was listed on the National Register of Historic Places in 1992. It now houses the Killingly Police Department.

The Danielson Main Street Historic District encompasses the historic late 19th-century commercial business district of the borough of Danielson in the town of Killingly, Connecticut. It extends along Main Street, between the Five Mile River and Spring Street, including a few buildings on adjacent side streets, representing the area's growth as a commercial and civic center in the late 19th and early 20th centuries. It was listed on the National Register of Historic Places in 1992.

Quinebaug Mill–Quebec Square Historic District is a historic district roughly bounded by the Quinebaug River, Quebec Square, and Elm and S. Main Streets in the town of Brooklyn (extending partly into the town of Killingly) in Windham County, Connecticut. The district encompasses a well-preserved 19th-century mill village. It was added to the National Register of Historic Places in 1985.

Temple Beth Israel is an historic former Orthodox and Conservative Jewish synagogue building, located at 39 Killingly Drive in the Danielson village of Killingly, Connecticut, in the United States. Built between 1951 and 1961 to a design by Boston, Massachusetts architect William Riseman, it is one of the first Modernist synagogues built in Connecticut. It was built in part by members of its congregation, many of whom were survivors of The Holocaust, and was formally dedicated on June 5, 1961 after ten years of construction. The congregation was a mix of Orthodox and Conservative adherents, and was merged with a congregation in Putnam in 2003. The building was listed on the National Register of Historic Places in 2013, and it has served as a cultural historical center, managed by a non-profit organization since 2009.

Broad Street – Davis Park Historic District is a historic district in the borough of Danielson, in the town of Killingly, Connecticut. The district is mainly residential in character, and includes Davis Park, a 1.9-acre (0.77 ha) triangular park created in 1890 and bounded by Main, Reynolds, and Broad Streets. The district as a whole is 30 acres (12 ha) in size. It includes examples of Stick/Eastlake, Queen Anne, and Colonial Revival architectural styles and was added to the National Register of Historic Places in 1998. It includes 95 contributing buildings, one contributing site, and four contributing objects. The district is significant for its architecture, which includes many examples of Victorian architecture with rich detailing. The buildings in the district also reflect the institutions and people responsible with the development of Danielson. The town's growth began in 1809, when brothers James and Hezekiah Danielson built a cotton spinning mill. The house of Hezekiah, built about 1825, is the oldest building in the district. The village's growth was further fueled by other textile mills, the completion of the Norwich and Worcester Railroad through town in 1830, the establishment of other businesses, and the expansion of the textile mills from the 1850s onward. The houses in the Broad Street-Davis Park area were built by middle and upper-class residents, who chose the latest architectural styles and built large houses. The area also was above the river terrace, providing fine views and flood protection.: 12–13 It includes the Old Killingly High School building, which is separately listed on the National Register, and two churches: the 1891 Gothic St. Alban's Church, and the 1960s Baptist Church, the latter of which is not historically significant.

Danielson is a borough in the town of Killingly in Windham County, Connecticut, United States. The population was 4,155 at the 2020 census.

East Brooklyn is a census-designated place (CDP) located within the town of Brooklyn in Windham County, Connecticut. It is the portion of the Danielson urban cluster within the town of Brooklyn. The population was 2,205 at the 2020 census. US 6 runs through the town and severs the town. The portion of the CDP near the Quinebaug River is known as the Quinebaug Mill-Quebec Square Historic District.

The Five Mile River is a 23.5-mile-long (37.8 km) river located in Connecticut's northeast corner which flows through the towns of Thompson, Putnam, and Killingly. The original Nipmuc name was Assawaga, meaning "place between" or "halfway place". The Assawaga received its English name from the fact that the first land laid out upon it was "supposed to be about five miles from" Woodstock, Connecticut. The Five Mile is a tributary of the Quinebaug River and is part of the Thames River watershed. Its source is Little Pond (also known as Schoolhouse Pond), close to the Massachusetts border. It empties into the Quinebaug River at Danielson, near the intersection of Connecticut Route 12 and U.S. Route 6. The Five Mile River has several dams, most of which are remnants of defunct mills and some of which are still used by local industry. Its largest impoundment is Quaddick Reservoir. The best examples of surviving mill villages are Killingly in villages such as Pineville, Ballouville, Attawaugan, and Dayville.

The Old Westfield Cemetery is located at 320 North Street in the Danielson borough of Killingly, Connecticut. The cemetery was established in 1720, not long after Killingly's incorporation (1708). It occupies a 10-acre (4.0 ha) parcel on the north side of North Street, and is bounded in part by the Five Mile River. Its main entry is marked by granite pillars placed in 1920, giving access to a perimeter road. The cemetery is laid out in a form typical of 18th-century and early 19th-century, with graves lined up in relatively even rows, avoiding the mid-19th century rural cemetery movement. Most of its 450 graves date to the 19th century. The cemetery was listed on the National Register of Historic Places in 2010.Killingly was settled in 1707, when James Daniels purchased the area between the Quinebaug River and the Rhode Island border from James Fitch. Daniels is considered the founder of the village of Danielson, and is buried in this cemetery. It was laid out in 1728, and remained in continuous use until about 1900, when additional space on the south side of North Street was added. Most burials now take place in the modern southern parcel, although burials still take place in family plots in the old section. About 15% of the graves date to the 18th century, typically with slate stones carved with cherubs or winged soul effigies. The larger number of 19th-century burials have a wider variety of monuments, including the use of granite and marble. The most elaborate family monument is that of the Atwoods in the northeast quadrant, which features a Classical statue and drapery.

Harvard H. Ellis Technical High School, or Ellis Tech, is a technical high school located in Danielson, Connecticut. It is part of the Connecticut Technical Education and Career System. Founded in 1916 as the Putnam Trade School, it was the first technical school in Connecticut to have its own building. It is in the Connecticut Technical High School System. It receives students from many nearby towns.The current school building was constructed in 2014. The building underwent renovations to add 30,000 square feet of new floor space as well as a new gymnasium, a classroom wing, a media center, and a culinary arts program space.

Old Furnace State Park is a public recreation area adjacent to Ross Pond State Park in the town of Killingly, Connecticut. The state parks covers 367 acres (149 ha), sits at an elevation of 390 feet (120 m), and is open year-round for hiking, hunting, and fishing. It is located east of Interstate 395, south of U.S. Route 6 and north of Connecticut Route 695. The park is the site of a former iron furnace. It was established as a town park in 1909 before being transferred to the state in 1918.

Quinebaug Lake State Park is a public recreation area covering 181 acres (73 ha) in the town of Killingly, Connecticut. The state park offers opportunities for fishing and non-motorized boating on Wauregan Reservoir. The park is managed by the Connecticut Department of Energy and Environmental Protection.