I am going to catalog the results above because comments sometimes get deleted, and are not intended to be part of the permanent record for a question.
- The Online Books Page for Charles Kingston O'Mahoney, 1884-
- All entries for the name O'Mahoney at GravestonePhotos.com
- Charles Kingston O'Mahoney grave monument details (now 1884-1944)
- Project Gutenberg: The Viceroys of Ireland by Charles Kingston O'Mahoney
- Detective novels by Charles Kingston (noted on site as also Charles Kingston O'Mahoney)
- 1920 US Census lists a Charles Omahoney, born about 1884, living in Bronx, NY
- 1930 US Census lists a Charles O'Mahoney, spouse Helen O'Mahoney, born about 1882, living in Bronx NY
Update - from an anonymous contributor:
Charles O'Mahony in the 1930 US Census Bronx NY is my mother's uncle. He was married to Helen Zacbek. He was born in Nenagh, Co. Tipperary, Ireland 1881 and died in the Bronx NY 1942. He is not Charles Kingston O'Mahony.
Seamus Murray Dublin