Your Jeremy Corwin was Jeremiah Corwin, son of Matthias Corwin and his first wife, Mary?) Aldrich. He was identified in the 1778 list as Jeremiah Corwin, 45, carpenter, born 1733. When Samuel Curwen visited Southold in 1755 he described Jeremiah as second son of Matthias.
He married Mary Gardiner in the First Church of Southold on 29 September 1757, but her name was erroneously given as "Gard" in Salmon (NY Biog & Geneal Reg, 49 (1918) 161. Although you say that died in 1821, ETC's 1872 Corwin genealogy says that his first wife died on 23 October 1798 and that he married (2) in 1800 Abigail _____. I suspect that your belief that Mary Gardiner died in 1821 can be traced back to some record saying that his wife died in that year and someone's jumping to a conclusion that she was his first wife. My notes indicate that in 1800 Jeremiah Corwin married Abigail Overton, but the only Abigail Overton I could identify was not born until 1784 and the 1820 census shows that his then wife was over 45. If his first wife died in 1798, leaving him a widower, he almost certainly married a widow Abigail Overton. I made no attempt to see if that was possible, but it would make sense to suspect that if there was an Abigail Overton born in 1784 there was also an older Abigail Overton in the vicinity.