The states of New Jersey, Pennsylvania, New York, Connecticut, Rhode Island, Massachusetts, Vermont, New Hampshire and Maine comprise the Northeastern United States. The story of Christianity in the region is one of shifting global and regional migrations entangled in European imperialist expansion and its aftermath. From the turn of the twentieth century, mass Western and then global urbanisation began to transform Christianity in the Northeast. Settler colonialism from Western Europe introduced a diverse array of post-Reformation traditions to the area. Missionary endeavours to the Native American population remained mostly peripheral to the colonial projects, aside from notable initiatives from Puritan John Eliot and French Jesuits led by Jean de Brébeuf. European diseases, along with occasional military conflicts, cleared most of the Native population from the region. The First and, especially, Second Great Awakenings of the eighteenth and nineteenth centuries further Christianised the region's European and small African-descendant population. Expanding mercantile connections combined with religious revival made the Northeast the nation's missionary-sending centre across the nineteenth and early twentieth centuries. Revival fervour and migratory mixing generated an environment of religious creativity and conflict, producing figures like Charles Grandison Finney and Sojourner Truth, as well as movements like Mormonism, led by Joseph Smith, that which became the Jehovah's Witnesses, led by Charles Taze Russell, and the Christian Scientist Association, led by Mary Baker Eddy. The movements coincided with Catholic migrations to Northeastern cities, migrations that maintained while also diversifying the region's Christian population. The religious tumult of the nineteenth century produced groups that migrated out of the area, like Smith and the Mormons. Others, including the Jehovah's Witnesses and Christian Scientists, maintain their international headquarters in the region to this day.

From the last century until the present, the Northeast remains a place of religious creativity and contradictions. The region is a centre of de-Christianisation, containing the nation's least Christian region, Northern New England. Countless urban neighbourhoods, conversely, are hubs of Pentecostal revival and Christian pluralisation. In the twentieth century, migration patterns shifted from east–west transatlantic crossings to north– south hemispheric entanglements, connecting urbanising populations from the American South, the Caribbean and Latin America to the Northeast's deindustrialising and depopulating cities. More than in any other global region, religious developments in the Caribbean continue to shape Christianity in the urban Northeast.