Particularly with information on the state of the language through the 19th century, what're some good books? I'm interested in its decline and causes of decline in Ireland at the time, as well as its attempted revival.
Mac Giolla ChrÃost (2005) is pretty much what you are looking for. It is a through study of both the history and the contemporary state of Irish on the island Ireland as a whole.
An excellent companion would be Crowley (2000), which is a collection of primary sources on language in Ireland from 1366 to 1922.