Jayne,
The surname Calvert is common in the Killyleagh area. There was a Hamilton Calvert in Killyleagh in the 1901 census. He?s not old enough to be your family but it is indicative that the name was in use in the area. He?s probably related somehow.
http://www.census.nationalarchives.ie/pages/1901/Down/Killyleagh/High_Street/1230847/
He gets a mention on the Ros Davies site:
of Tullymacknows; son of William Calvert; married Ann McMurray 29 Mar 1862 in Killinchy ; father of James b. 6 Nov 1867 & Sarah b. 16 Jun 1870 & Mary Jane b. 1 Oct 1872 (regd. Killyleagh); died 24 Jun 1901; buried Killyleagh Presbyterian graveyard
http://freepages.genealogy.rootsweb.ancestry.com/%7Erosdavies/
I assume your family were Presbyterian. Killyleagh 1st Presbyterian church has baptism records for 1693 -1757 and 1835 to 1881. Marriages 1692 ? 1757 & 1833 ? 1851 & 1854 ? 72. So you might find your family there. The baptisms 1835 to 1882 are on-line on the rootsireland site (subscription). The marriages are not. Copies of the baptisms and marriages are kept in PRONI (the public record office) in Belfast. A personal visit is required to access them.
Elwyn
