The following information is taken from the Dictionary of the Older Scottish Tongue, available online at http://www.dsl.ac.uk/index.html. This is a work in progress.
| Spelling | Number | Dates & headers |
|---|---|---|
| Mortoun | 4 | 1478 (cousing); 1570 (chanslar); 1571 (chancelar); 1588 (chefely) |
| Morton | 1 | 1638 (cowper) |
| Mortone | 1 | 1574 (cum) |
| Mortoune | 1 | 1631 (collig) |
| Mourtoun | 1 | 1566 (deacon) |
| Murtoun | 1 | 1566 (darg) |