Kenneth Libo, a historian of Jewish immigration who, as a graduate student working for Irving Howe in the 1960s and ’70s, unearthed historical documentation that informed and shaped “World of Our Fathers,” Mr. Howe’s landmark 1976 history of the East European Jewish migration to America, died on March 29 in New York. He was 74.

The cause was complications from an infection, said Michael Skakun, a friend and fellow historian.

Mr. Libo’s contribution was acknowledged by Mr. Howe and the publishers of “World of Our Fathers,” who listed his name beneath the author’s on the cover of the book: “With the Assistance of Kenneth Libo.”...