| Abbreviation | Definition |
|---|---|
| SR | Sister |
| SRGP | Sullivan Rutland Genealogy Project |
| ST | State |
| STWG | Southern Tier Winter Guard |
| sur | surety |
| SUVCW | Sons of Union Veterans of the Civil War |
| TAG | The American Genealogist |
| ten | tenant |
| TERR | TERRitory |
| TEST | Testament (witness) |
| test | witness |
| THAGS | The Humble Area Genealogy Society |
| TIARA | The Irish Ancestral Research Association |
| TIGS | Troy Irish Genealogy Society |
| UA | Ultimate Ancestor |
| UCGA | Upper Cumberland Genealogical Association |
| ult | ultimo (late) |
| un | unknown |
| unm | unmarried |
| UNM | UN-Married |