The ‘green flag’ regiments of the Union army remain the most recognisable expression of Irish involvement in the American Civil War. These ethnic Irish units were proud of their heritage and sought to combine this with their loyalty to Union, often by carrying green flags amongst their colours or bearing epithets such as the ‘Irish Brigade.’ But where were these ‘Irish’ soldiers from? How many of the men were Irish emigrants, how many were Irish-American, and how many had no connection to Ireland? A number of posts on the site have explored this issue as it relates to the 23rd Illinois Infantry (Mulligan’s Irish Brigade) and the 90th Illinois Infantry (Chicago’s Irish Legion) and the data complied from this analysis is presented here as a resource. Click on either of the regiments below to see their nativity data represented graphically.