The irish that immigrated to the united states in the mid 1850s tended to live in

They lived in Tenements

Explanation:

A tenement is a building that is occupied by more people or families than a house. In the United States often people referred to old and rundown buildings as tenements. So since Irish immigrants were not that rich they used to occupy those rundown buildings. But not only the Irish lived there and in New York in 1865 over 500 000 people lived in tenements.