In Katherine Paterson's Lyddie, which ethnic group is receiving most employment at the Concord Corporation?

More and more Irish immigrants are coming to work at the Concord Corporation. The factory likes being able to hire the Irish because they don't room in the company boarding houses, so the company saves money by employing them. Even very young children from Irish families work at the Concord Corporation; children as young as seven or eight years old work as doffers.

The Irish families live in a very poor part of town called the Acre, where their homes are nothing more than shacks, despite the fact that the immigrants tend to have large families with up to a dozen children. The Irish are looked down upon because of their poverty, their poor dress, their body odor, their language, and their religion. Lyddie thinks of them as "papists"--meaning that they are Catholic rather than Protestant--a derogatory term Lyddie uses even though she herself is not particularly religious.

Lyddie at first has very little patience for training Brigid, her Irish coworker, not only because she doesn't want to decrease her own production at the factory, but also because she harbors prejudices against her ethnicity. She doesn't like the thought of placing her mouth over the hole of the quill where Brigid has put her mouth. In fact, Lyddie does end up getting sick, presumably from Brigid, whose mother is very ill. This shows how the immigrant population was more prone to illness because of the relative squalor in which they lived. When Lyddie visits Brigid's home after Lyddie gets dismissed, she finds the home to be messy and smelly with only beds to sit on. 

The novel reflects the historical reality of the influx of Irish immigrants during the potato famine from 1845 to 1855. The immigrants lived in slum-like areas of cities, especially in the manufacturing towns of the Northeast. Although they faced extreme discrimination at first, they soon assimilated into American society and became valued members in the same way Brigid shows herself to be a valuable friend to Lyddie. Education helped the Irish families rise out of poverty, and in 1960 the great-grandson of an Irish immigrant who had fled the potato famine, John F. Kennedy, became President of the United States.