Looking for Hugh Walker and Mary (Richards) Walker

Hello, Please help me find information on Hugh Walker, born in Ireland, 1802.  He married Mary Richards, after she arrived in America, who was born in Ireland, 1812.  These dates are according to their headstones, here in Daleville, Indiana, USA.  I have a photo of a thatched roof house with the caption, Cousin James Walker's home in County Antrim Ireland. The town of Coleraine is also noted on the picture.  I found a ships manefest and I think it shows when Hugh Walker and his parents and siblings came over from Ireland.  It is the Robert Fulton and it sailed from Belfast on 28, September, 1820. I know of at least 1 place where it docked, Charleston, South Carolina on 3, November 1820.  The manefest lists David Walker aged 33, Mary Walker aged 33, Isabella Walker 18, Hugh Walker 9, and John Walker 7.  There is also and Isaac Walker, 26, but I do not know if he is related or not.  I believe Hugh Walker married Mary Richards in Clinton, Ohio, USA on March 28, 1838.  I have no information on the Walkers between 29/9/1820 and 28/3/1838.  Any help and information you may have is greatly appreciated.  I am not sure if I am even going down the correct "path" with these names and dates.  Thank you very much, Carol