Fiona:
!901 census is earliest available for Down. I took a quick look at a head-of -household index on Caora
http://www.caora.net/find.php and found some listings for Kelly in Dromore. Not much help if you don't know parents' names or unless they never married. Anyway, here they are:
Joseph Kelly Ballysallagh Dromore 1901_Census Skeagh Division
Samuel Kelly Ballysallagh Dromore 1901_Census Skeagh Division
William Kelly Ballysallagh Dromore 1901_Census Skeagh Division
John Kelly Dromore Village Meeting Street Dromore 1901_Census Dromore Urban
John Kelly Dromore Village Meeting Street Dromore 1901_Census Dromore Urban
Martha Kelly Dromore Village Meeting Street Dromore 1901_Census Dromore Urban
Rebecca Kelly Dromore Village Mount Stewart Dromore 1901_Census Dromore Urban
Prudence Kelly Ednego Dromore 1901_Census Skeagh Division
Joseph Kelly Greenan Dromore 1901_Census Quilly Division
Guy Kelly Leapoks Dromore Tithes_1834
John Kelly Leapoks Dromore Tithes_1834
Hugh Kelly Marabeg Dromore Tithes_1834
Sarah Kelly Quilly Dromore 1901_Census Quilly Division
William Kelly Tullindoney Dromore Tithes_1834
Alexander Kelly Tullindoney Dromore 1901_Census Skeagh Division
Thomas Kelly Tullymacarville Dromore 1901_Census Quilly Division
James Kelly Tirfergus Drumballyroney 1901_Census Tirkelly Division
Good luck,
Pat