March is Irish American Heritage Month and Greek-American Heritage Month.
October is National Italian American Heritage Month, and German American Heritage Month. [Source: U.S. Customs and Border Protection Diversity and Inclusion page. Scroll down to the chart.]

Library of Congress, Prints & Photographs Reading Room. Date Created/Published: [between ca. 1907 and 1921]
Gale Encyclopedia of Multicultural America
by
This work provides essays on specific minority and ethnic groups in the U.S., with an emphasis on culture (religions, holidays, customs, language), historical background, and settlement patterns. Ethnoreligious groups such as Jews, Chaldeans, and Amish are included. Each essay has a listing of organizations and research centers, names, addresses, and contact information for periodicals, media, and suggestions for further reading.
Use the databases listed under the Research tab to find articles.