The Middletown Chapter of Alpha Delta Phi was the nineteenth in order of the establishment, receiving its Charter on July 31, 1856, and holding its first regular meeting on Saturday evening, August 2. It sprang from the union of two local societies, the Betrians and Lebanians. The Betrian Society was organized in 1847, from an older association, the Alpha Psi. The Lebanian Society began in 1854. For about a year after 1855, both the Betrians and Lebanians patronized the Chronometer Eating Club and the gastronomic fellowship, thus established, somewhat neutralized the rivalry.
The Convention of Alpha Delta Phi in 1856 was held in New Haven and representatives of each society presented separate petitions for charters. Until the fact was disclosed at the Convention, neither society knew that the other was considering a petition to Alpha Delta Phi. Their respective supporters in the Fraternity split the Convention. Neither party was powerful enough to defeat the other and a union was proposed. The united societies were initiated into Alpha Delta Phi at the McDonough House in Middletown, Connecticut, on the evening of July 31, 1856. The 1956 Convention, held at Wesleyan, was in part a celebration of the centennial of the Chapter.
The alumni organization, The Adelphic Literary Society was incorporated in 1881 to purchase property and construct a permanent home for the Chapter. The new Lodge Room was dedicated on May 29, 1884 during the 52nd Convention, and the House was completed the following year. The present House was begun on the same site in 1904 and completed in 1906.
In 1944, a group of alumni organized the Adelphic Educational Fund, a tax-exempt foundation to support the scholarship and literary program, which was already a tradition at the Chapter. Possessed of a substantial endowment, the Fund has encouraged the growth of an extraordinary range of activities.
The Adelphic Aid Program, founded in 1946, had made grants to numerous Wesleyan students totaling an amount approaching a quarter of a million dollars. The Adelphic Library Program began making grants in 1947 for books, classical records, and magazines.
In 1969 Wesleyan University began admitting women.
The Fraternity made the Chapter inactive in 1992.