The North Country of New York was inhabited by the Iroquois/Haudenosaunee Native Americans when the first French, Dutch, and English fur-traders arrived in the 1600s.

[4] Richard Coote, the first colonial governor, passed a law at the end of the 17th century that mandated a life sentence to any Catholic priest.

"[4]However, much of the North Country was still disputed territory between France and Great Britain, allowing Catholics more freedom to reside there.

In 1749, the Sulpician Abbé François Picquet traveled from Montreal to establish the Mission of The Holy Trinity at Fort de La Présentation near present-day Ogdensburg.

[7] In 1818, Jacques Leray, son of Count Jacques-Donatien Le Ray de Chaumont, established a colony of French and German Catholics in Jefferson County.

At the same time, Irish and French Canadian immigrants began to arrive, prompting the diocese to found missions for them.

[9] The establishment of mills and factories in the North Country attracted a large influx of Irish Catholic immigrants.

The diocese then established new missions at Antwerp, Belleville, and Canton; and parishes at Cape Vincent, Hogansburg, and Keeseville.

In 1860, Bishop John McCloskey of Albany placed the parish at Carthage under interdict for two years when violent confrontations erupted among the parishioners.

[11] One of Wadham's first projects was to expand the small St. Mary's Church in Ogdensburg into a proper cathedral, adding a sacristy, stained glass windows and a sanctuary.

Gabriels was responsible for the growth and development of the Catholic Summer School at Cliff Haven near Plattsburgh, serving 10,000 people annually.

Pope Pius XII then selected Reverend Bryan McEntegart from the Archdiocese of New York to replace Monaghan.

During his short tenure, Kellenberg expanded the diocese's Departments of Education and Catechetics and increased the number of parochial schools.

John Paul II replaced Loverde in Ogdensburg with Auxiliary Bishop Gerald Barbarito of the Diocese of Brooklyn that same year.

In 1979, Reverend Liam O'Doherty of St. Ann's Church in St. Regis Falls was indicted on sexual abuse charges involving three 14-year-old girls.

[31] Reverend John J. Fallon of Holy Angels Parish in Altona was arrested in September 1985 on charges of mailing child pornography.

In May 2018, Bishop LaValley expressed his opposition to the proposed New York Child Victims Act, which created a one-year window for adults to sue for sexual abuse crimes.

In an interview, LaValley made this comment about the scandal:[35]"The Church screwed up big time and people have been hurt immeasurably.

[36] By the time that the Child Victims Act has passed, the diocese had already paid nearly $5.5 million to settle previous lawsuits, and held in healing masses and reconciliation therapy as well.

[37] In February 2020, diocesan communications director Darcy Fargo revealed that the diocese was considering Chapter 11 bankruptcy due to dozens of pending sex abuse lawsuits.

She stated that "Chapter 11 reorganization has been a positive vehicle through which other dioceses have been able to address the needs of claims while continuing to undertake their vital mission as church.

"[37]In May 2020, Cuomo extended the Child Victims Act's statute of limitation deadline to file sex abuse lawsuits from August 2020, to January 2021.