Area codes 203 and 475

New Haven County is a county in the south central part of the U.S. state of Connecticut. As of the 2020 census, the population was 864,835, making it the third-most populous county in Connecticut. Two of the state's top 5 largest cities, New Haven (3rd) and Waterbury (5th), are part of New Haven County. New Haven County is part of the New Haven-Milford, CT Metropolitan Statistical Area, which is included in the New York metropolitan Combined Statistical Area. County governments were abolished in Connecticut in 1960. Thus, as is the case with all eight of Connecticut's counties, there is no county government, and no county seat. Until 1960, the city of New Haven was the county seat. In Connecticut, towns are responsible for all local government activities, including fire and rescue, snow removal and schools. In some cases, neighboring towns will share certain activities, e.g. schools, health, etc. New Haven County is merely a group of towns on a map, and has no specific government authority. The county Sheriff system was abolished by voters and replaced by State Judicial Marshals in 2000. As a result, the state judicial system in New Haven County has three judicial districts: New Haven, Ansonia-Milford, and Waterbury. On June 6, 2022, the U.S. Census Bureau formally recognized Connecticut's nine councils of governments as county equivalents instead of the state's eight counties. Connecticut's eight historical counties continue to exist in name only, and are no longer considered for statistical purposes.

Congregation Mishkan Israel, in Hamden, Connecticut, is the oldest Jewish congregation in Connecticut, the 14th oldest continuous operating synagogue in America as well as the oldest continuing synagogue in New England. It was founded by 15 to 20 New Haven Jewish families, mostly from Bavaria, in 1840, when Jews were not allowed to form their own religious societies. These families took turns hosting services and event at their homes until the Connecticut Legislature, in 1843, enabled Jews to officially establish synagogues by allowing non-Christian organizations to incorporate in the state. Mishkan Israel's first gatherings were held in a room above the Heller-Mendelbaum store at the corner of Grand and State Street in New Haven, Connecticut. This did not sit well with the New Haven Register, which reported on May 26, 1843: “Whilst we have been busy converting the Jews in other lands, they have outflanked us here, and effected a footing in the very centre of our own fortress.”It became a Reform synagogue as early as 1856. Also in 1856 the congregation purchased the former Third Congregation Church, a Greek revival building on Court Street between State and Orange Street. The 1897 building, 55 Audubon Street on the corner of Orange Street in New Haven is now used as a performing arts space for ACES Educational Center for the Arts, a performing arts high school. It is a contributing building in the Orange Street Historic District. The architects were Arnold W. Brunner and Thomas Tryon. The congregation moved to Ridge Road in Hamden in 1960. The Ridge Road campus was listed on the National Register in 2021.Mishkan Israel became a bastion of liberal religious thought and social activism in the 1950s and 1960s. Then Rabbi Robert E. Goldburg was an outspoken advocate for civil rights, and was arrested in a freedom march along with Martin Luther King and other clergy in 1964. Earlier, Dr. King had delivered a sermon at Mishkan Israel in 1961, helping to dedicate the new facility, which had relocated to Hamden. It is said to have been Dr. King's only preaching from a pulpit in the greater New Haven area. Rabbi Goldburg stirred congregants’ passions with his strong and eloquent political voice raised frequently in support of racial justice and opposition to the Vietnam War. Dr. Daniel Ellsberg, Alger Hiss, Stokely Carmichael, and William Sloan Coffin were guest speakers at the behest of Rabbi Goldburg. Marilyn Monroe converted to Judaism at CMI during Rabbi Goldburg's tenure. The current rabbi at Mishkan Israel is Brian P. Immerman, who has served Mishkan Israel since 2018. He succeeds Rabbi Herbert N. Brockman, now the Emeritus, who had been the spiritual leader at Mishkan Israel for over 30 years. Rabbi Brockman teaches and engages in community projects, and has been at the forefront of interfaith understanding and justice, not only in New Haven, but also nationally and internationally. The current Cantor is Arthur Giglio, who holds a Master of Sacred Music and Diploma of Hazzan from The Jewish Theological Seminary. Rabbi Brockman decided that a fitting tribute to Rabbi Goldburg and Martin Luther King's historic connection to Mishkan Israel would be an annual Martin Luther King Interfaith Service which he inaugurated in 2010. The late peace activist Bruce M. Cohen served as rabbi of Mishkan Israel prior to founding Interns for Peace.

New Haven Country Club is a private country club located in Hamden, Connecticut. Founded in 1898 NHCC is one of the oldest golf courses in America. The club was founded as the New Haven Golf Club in downtown New Haven and then moved to newly purchased farmland along Lake Whitney in Hamden later. Notable early members include President William Taft, Walter Camp, Eli Whitney III, Henry Sargent, Frank Bigelow, Winthrop Bushnell, Charles C Claire, and Henry Hotchkiss. The club's PGA Head Golf Professional is William Wallis. The original golf course was completely redesigned in 1921 by two-time Open Champion Willie Park Jr., incorporating the natural elevation changes of the 110-acre plot. In recent years thousands of trees have been cut down to restore the original vistas of Lake Whitney. New Haven Country Club's distinctively fast and large greens are a defining feature of the course. Del Kinney, the former executive director of the Connecticut State Golf Association remarked, “New Haven [Country Club] is very demanding and sneaky tough, but a very fair test. In fact, it’s the best in the state from the perspective of being both fun to play and challenging.”

Lake Whitney is a lake in Hamden, Connecticut, that is a part of the Mill River. The lake was a water source for the New Haven, Connecticut, metro area, until its associated treatment plant became antiquated in the 1990s. A new water treatment facility was constructed in the early 2000s rated for up to 15 million gallons per day. Lake Whitney now serves as one of four primary sources of surface water for the RWASouth Central Connecticut Regional Water Authority. RWA also operates a gravity release from the dam when there is no flow over the spillway, and operates an "Eel Pass" in conjunction with CT DEEP to assist with eel migration over the dam.

Spring Glen is a neighborhood in the southeastern portion of the town of Hamden, Connecticut. It is primarily residential, mostly single-family homes with a few two-family. Commercial development is entirely on its principal street, Whitney Avenue. It was developed throughout the first half of the twentieth century as a trolley suburb of New Haven. It was named for the Spring Glen dairy farm established by James J. Webb in 1858 in what would become part of the neighborhood.There are no officially established boundaries for the neighborhood. The Spring Glen Civic Association has it bounded on the north by Skiff Street, on the east by Hartford Turnpike, on the south by Waite Street (including three small streets extending a bit south of Waite), and on the west by Lake Whitney and Mill River. This definition includes a small portion of the adjoining town of North Haven. The census tract with GEOID 09009165500, corresponding closely to the Hamden portion of the neighborhood, had a population of 4,959, as of the 2010 census.

The Whitneyville Congregational Church, now the Whitneyville United Church of Christ, is a historic Congregational Church at 1247-1253 Whitney Avenue in the Whitneyville section of Hamden, Connecticut. The congregation is now affiliated with the United Church of Christ (UCC). The church building is a Greek Revival style built in 1834, with an interior altered in 1866 to designs by Rufus G. Russell. The church, along with its 1924 parish house, was added to the National Register of Historic Places in 1995 for its architecture.

The Pistol Factory Dwelling is a historic house at 1322 Whitney Avenue in Hamden, Connecticut. Built in 1845 and enlarged before 1860, it is an unusual example of a Greek Revival worker's boarding house, built by Eli Whitney II (son and business success to inventor Eli Whitney) to house workers at his nearby pistol factory. The house was listed on the National Register of Historic Places in 1991.

Hamden Hall Country Day School is a coeducational private day school in Hamden, Connecticut, educating students in preschool through grade 12. Hamden Hall was founded in 1912 as a country day school for boys by John P. Cushing, its first headmaster. It was the nation’s fourth country day school. The school has been coeducational since 1927 and expanded to include classes through grade 12 in 1934. Now split into three separate divisions, Hamden Hall enrolls the majority of its nearly 600 students in the upper and middle schools (Grades 7–12) and the remainder in the lower school (preschool through grade 6). Tuition (2022–2023 school year) ranges from $20,100 in PreSchool to $46,975 in grades 9–12. Hamden Hall awards need-based financial aid to approximately 30 percent of its student body. Hamden Hall is accredited by the New England Association of Schools and Colleges and is a member of National Association of Independent Schools and the Connecticut Association of Independent Schools.

The George Atwater House is a historic house at 1845 State Street in Hamden, Connecticut. Built about 1820, it is a good local example of a vernacular Federal period farmhouse, with a well-preserved interior and unusual floorplan. It was listed on the National Register of Historic Places in 1992.

The Eli Whitney Museum, in Hamden, Connecticut, is an experimental learning workshop for students, teachers, and families. The museum's main building is located on a portion of the Eli Whitney Gun Factory site, a gun factory erected by Eli Whitney in 1798. The museum focuses on teaching experiments that are the roots of design and invention, featuring hands-on building projects and exhibits on Whitney and A. C. Gilbert.

The Atwater-Linton House, also known historically as Appledore, is a historic house at 1804 State Street in Hamden, Connecticut. Built about 1781 by a descendant of one of the area's first settlers, it was the home of engraver and political activist William James Linton in the late 19th century. It was listed on the National Register of Historic Places in 1992.

Edgerton Park, also known as the Frederick F. Brewster Estate, is a 20-acre (8.1 ha) public park on Whitney Avenue, straddling the New Haven–Hamden town line in Connecticut. It is site of the demolished Victorian home of Eli Whitney II, known as "Ivy Nook". In 1909, it became the estate of industrialist Frederick F. Brewster, with a new Tudor-style mansion constructed named Edgerton for its location on the edge of town. The mansion was demolished in 1964, pursuant to Brewster's wishes, after the death of his wife, and the property was donated to the city. The present landscape was designed by Robert Storer Stephenson in 1909.: 4, 6 The property was listed as historic district on the National Register of Historic Places in 1988. In 1988, the district included seven contributing buildings, eight other contributing structures, and one contributing object.