The largest group of immigrants to make port in New Brunswick, during the first half of the 19th century, were the approximately 30,000 Irish, who fled their homeland in the 1840s and 1850s because of the potato famine. Only a portion of them stayed in Saint John; however, they, along with other Irish immigrants who had arrived the previous two decades, put a Celtic stamp on that city. In 1851, census takers recorded that half the port city's household heads were Irish.
The influx of thousands of poor Irish, in the 1840s, resulted in overcrowding in the city's core, as the newcomers found lodgings along the waterfront and main thoroughfares. Here they worked on the docks as longshoremen, as well as in sawmills, factories, and foundries, and most often as day labourers. By 1860, some of these poverty-stricken city dwellers were making plans to establish the rural community of Johnville, in Carleton County. Bishop John Sweeny, of Saint John, the settlement's primary promoter, argued that the forests of Carleton County offered them a better life and an escape from an unhealthy industrial environment.