There were lots of Cassidys in the Kilrea area. Two from extracted Irish births (www.familysearch.org)-
16 May 1869 Kilrea district parents- James Cassidy/Elizabeth Watt
31 May 1970 Kilrea district parents- Hugh Cassidy/Sarah Jane McCoey
The database is not complete so there could be others in this period.
Just a note, James Cassidy and Elizabeth Watt went to Greenock Scotland where Elizabeth passed away prior to 1875. I know this because he then married Mary Leech (also from Ireland) and became stepfather to my great grandfather. Of James and Elizabeth's four children born in Ireland, I've seen no evidence that the first three Mary, Nancy Jane or John lived out childhood. James and Elizabeth show up in census data with only the fourth child, Elizabeth, and my great grandfather, Thomas White.