Theta Delta Chi (ΘΔΧ) is a social fraternity that was founded in 1847 at Union College, New York, United States.

Theta Delta Chi brothers refer to their local organizations as charges rather than using the common fraternity nomenclature of chapters.

The Fonda brothers seemed to be under the impression that they were founders and the existence of this record led to the mistaken belief that Theta Delta Chi was founded in 1848.

Westward expansion had traditionally been opposed by a large segment of the Fraternity, which worried that supervision and solidarity would suffer if Theta Delta Chi were to stray far from the East.

The rise of the large state universities in the West, particularly in the Big Ten, eventually overcame that resistance and Michigan, Minnesota, and Wisconsin welcomed Theta Delta Chi between 1889 and 1895.

Berkeley (1900), Stanford (1903), the University of Washington (1913) and UCLA (1929) brought Theta Delta Chi in strength to the Pacific coast.

Expansion in the East during the 1870s, 1880s and 1890s brought Charges to Cornell, Boston University, Wabash, CCNY, Columbia, Lehigh, Amherst, Yale, MIT, Williams, and George Washington.

The 1881 Convention required that the President of the Grand Lodge visit every Charge once a year; Central Fraternity Office staff now performs these duties.

The financial health of Theta Delta Chi was ensured through the establishment of two entities, the Founders' Corporation in 1910 and the Educational Foundation in 1944.

[8] The 1992 rechartering at Wabash continued a pattern of reviving inactive Charges; new charterings in the 1990s and 2000 include Northeastern, Nova Southeastern, UNC Greensboro, SUNY Albany and Merrimack.

Theta Delta Chi has also worked to increase its presence in the northeast with the installation of the Iota Triton Charge at UMass Dartmouth in 2005.

A freshman student, Kenneth Patterson, attended the party and was later killed by an Amtrak train after stumbling onto the tracks while highly intoxicated.