| No. | Name | Type | Language | Counties |
|---|---|---|---|---|
| 1 | Christina Suzanne O'Neill | Master | English | All |
| 1 | ERIN JEAN O'REGAN | Master | English | Multnomah |
| 1 | Amie O'Rourke | Master | English | Benton, Linn |
| 0 | Kimberly Diane O'Shaughnessy | Community | English | Crook, Deschutes, Jefferson, Klamath |
| 0 | EZELMA ANN OBUHORO | Master | English | Multnomah, Washington |
| 11 | RUTH NOEMI OCHOA | Master | English, Spanish | All |
| 0 | TRISTA MICHELLE OCHOA | Master | All | |
| 0 | WHITNEY OCONNELL | Community | English | All |
| 0 | CATHERINE ANN OEHLER | Master | English | Clackamas, Multnomah, Washington |
| 22 | Soobin David Oh | Master | English | All |
| 117 | HEATHER OLEARY | Master | English | All |
| 1 | Katherine Elaine Olinger | Master | English | All |
| 0 | Yamel Olivas Solis | Standardized | Spanish | Clackamas, Multnomah, Washington, Yamhill |
| 0 | Diane Lynn Olney | Community | English | Washington |
| 0 | EUNICE BEVERLY OLSON | Standardized | English | Jackson, Josephine |
| 0 | Laura Ann Olson | Master | English | Clackamas, Marion, Multnomah, Polk, Yamhill |
| 0 | LINDA OLSON | Standardized | English | Umatilla |
| 19 | Kim (Kiki) Omoto | Master | English | Benton |
| 1 | LISSET ONEILL | Community | English, Spanish | Multnomah |
| 1 | Nancy Louise Orem | Master | English | All |