Agnes de Dammartin was born circa 1166 to Alberic II de Dammartin (-1200) and Mahaut de Clermont (1147-1200) . She married William I de Fiennes (c1160-c1240) .
Children
| Name | Birth | Death | Joined with |
| daughter de Fiennes (c1188-?) | |||
| Baldwin de Fiennes (c1190-?) | |||
| William de Fiennes (c1200-?) | |||
| Enguerrand II de Fiennes (c1210-1265) | 1210 | 1265 | Isabelle de Conde (c1214-) |
| Mahaut de Fiennes (c1210-aft1244) | 1210 | 1244 | Baudouin III de Guînes (1198-1244) |
Footnotes (including sources)
| ‡ General |
|