Article describing nativist, anti-Catholic sentiment in rural Massachusetts's Nashoba Valley in the nineteenth and early twentieth century - including the towns of Shirley, Groton, and Pepperell. Negative local attitudes toward Irish and French Canadian immigrants made explicit in religious and educational contexts in what was an historically, homogeneously Protesant region. Several instances of interreligious tolerance and amicability in the same region. World War I and the regional rise in size and influence of the Ku Klux Klan. Characterizations of the KKK in New England - particularly Massachusetts, and Groton therein - in the first decades of the twentieth century, with select examples of growth, assembly, and violent discrimination.