I took a look at census information, and CASSELY is not a popular name. In MA there are 2 people in middle MA in 1860 and 1870. There are 2 more people in the 1910 and 1920 census including:
CASSELY, PERCIVAL J (1910 U.S. Census)
MASSACHUSETTS , ESSEX, 5-WD LYNN
Age: 36, Male, Race: WHITE, Born: CANA
Series: T624 Roll: 584 Page: 73
He lived with his wife, Marie, and he was a house painter, and came down from CAN-ENG in 1886.
CASSELY, WILLIAM F (1910 U.S. Census)
MASSACHUSETTS , SUFFOLK, 12-WD BOSTON
Age: 34, Male, Race: WHITE, Born: CANA
Series: T624 Roll: 618 Page: 117
He was a lodger in someone's home, and he worked in a shop. He also came down from CAN-ENG in 1870's.
CASSELY, PETER (1920 U.S. Census)
MASSACHUSETTS , ESSEX, 4-WD LYNN
Age: 47, Male, Race: WHITE, Born: CANA
Series: T625 Roll: 694 Page: 208
It looks like Percival and Peter are the same person.
The people who were in MA in 1860 and 1870 had been born in Ireland.
Have you checked the archives of the MA Lists and Boards to see if anyone else is researching the name?
(I cannot check the 1930 census but other people can.)
Betty (near Lowell, MA)