Simeon was born in 1743. Simeon's parents, Cuffee and Flora, were African American people enslaved by Scituate residents Deacon Joseph Clapp and Thomas Clapp respectively.
Simeon and his brother Charles Granderson moved to Adams in Western Massachusetts and enlisted in the Revolutionary Army there. They resided in a neighborhood called "New Providence" and Simeon appears there after the war in the 1790 U.S. Census. Later, the brothers returned to Scituate, settling in the part of town that became Norwell on land that may have been property deeded to the brothers' parents after they gained their freedom.
Here is a transcription of Simeon's service in Massachusetts Soldiers and Sailors of the Revolutionary War:
GRANDISON, SIMEON, New Providence (also given Adams). Private, Col. Seth Warner's regt.; Continental Army pay accounts for service from Feb. 14, 1777, to Feb. 14, 1780; residence, New Providence (also given Adams); also, return dated Fort George, June 11, 1780, of officers and men belonging to Massachusetts in Col. Seth Warner's regt.; enlisted Feb. 14, 1777; enlistment, 3 years; reported discharged Feb. 14, 1780.
When Simeon returned after the war, locals noted that he returned with a white wife. A local history written in 1928 recounts:
It was rumored that [Granderson and his wife] came from the western part of the State and the man had served in the Continental army from the town of Adams. Paying no heed to their neighbors they proceeded to set up an establishment. The land was cleared and gradually people ceased to wonder about them and they lived their lives and ended their days in their little place in the woods. 
Simeon died in Scituate 1835. There is only one Simeon Grandison in the "Massachusetts Soldiers and Sailors" books and only one Simeon Grandison in the Revolutionary War pension rolls. The death date of May 23, 1835, in Simeon's pension record matches the death date of Simeon Granderson in the Vital Records of Scituate, therefore Simeon of Scituate/Norwell is the Simeon who resided in Adams and fought for the Revolutionary Army.
An independent documentary was made about how Simeon's family was the inspiration for the names of two landmarks in town and provided many of the genealogical sources leads for this profile: WATCH: The Cuffee Origin.
Cuff(e) and Charles Granderson/Grandison appear to be the same person. He is not to be confused with his father, also named Cuffee, or Simeon's son, also named Charles. It seems that Charles is used in Granderson's military records and Cuffe is used in Scituate's records.
Brothers Charles and Simeon Granderson appear in Merrit's "Old Time Anecdotes of the North River and the South Shore," but Merrit apparently conflated the two men and attributes some of Simeon's biography to Cuffee. Merrit quotes that "Cuff Grandison died in 1810," but Simeon's death record shows him dying in 1835.Therefore Charles must be Cuffe Granderson.
UPDATE 12 Feb 2023: I now believe that both Charles and Simeon were referred to as some version of Cuff/Cuffee in Scituate records and historians. - WT