Hi, Found some info on Dennis Regan in the US civil war pensions database:
Residence: Holliston, Massachusetts Occupation: Laborer
Service Record:
Wounded (In 1864)
Enlisted as a Private on 05 January 1864 at the age of 42
Enlisted in Company H, 1st Cavalry Regiment Massachusetts on 05 January 1864.
Mustered out Company H, 1st Cavalry Regiment Massachusetts on 17 June 1865
Do you know of any regans from county claire, Ireland? Let me know. Thanks.