I have a 1790 census report O. D. Allen Yamasee Dist. 1 son under 10,1 son 16-26, 1 to age 45, 1 dau, up to 26 and 1 female 45 and over. Also I've seen his name written Orasmus D. Allen, Clerk of Court, born in 1774. (dates vary). 1st wife Harriet Duncan, dau. of Capt. Joseph Duncan and wife Harriet W. Jennings, 2nd wife Rebecca Stokes.Died Dec. 3rd 1847 buried at Baptist Cemetery, Barnwell. He was the son of Sherwood Allen, b. abt. 1740 in Colleton Co, SC. Died aft. 1790 Richmond Co. Ga. married Mary Cargill Sherwood Allen was the son of Josiah Allen Sr. born about 1720 in Scotland or Ireland died in Green Co. Ga..He married in 1740 in Collecton Dist. SC, Unknown. One book called Biographical Sketches lists him as Orsamus D. Allen 1838-1839 , Commissioner in Equity
Hope this helps. My Allen family is from Barnwell, haven't made the connection yet!