I recently attended a presentation that was given by the Orange County Historian, Cornelia Bush. She gave several reasons for the migration of this group of people from Southold to Orange County.
1. The desire to spread their Calvinist-inspired gospel among the Indians. This was a group of austere Protestants that can be traced back through time to the Massachusetts Bay and before that, ultimately, to members of the congregation of St Edmund's Church, Southwold, Suffolk, England. According to Wikipedia, "Southwold was the home of a number of Puritan emigrants to the Massachusetts Bay Colony in the 1630s, notably a party of 18 assembled under Rev. Young, which travelled in the Mary Ann in 1637." Those followers of Rev. Young/Yonge are our ancestors who stayed together for over 150 years from Southwold to Massachusetts Bay Colony to Southold LI, in the Province of New Haven, to Orange County. It's quite amazing.
2. There was a drought on Long Island from about 1750 to 1752.
3. The large patents in Orange County were re-drawn in the last half of the 18th century into much smaller lots that many average persons could afford.
This group of Calvinists belonged primarily to the Protestant and Congregational Churches, frequently treating them as interchangeable.
The group began scattering from Long Island during the Revolutionary War. Most fled to Connecticut for the duration (see "The refugees of 1776 from Long Island to Connecticut" on Archives.org http://archive.org/details/refugeesof1776fr00mathuoft
). Some stayed in Connecticut after the War, some returned to Southold, some migrated to Orange County, and for the Loyalists amongst them, they went to Nova Scotia.