A by-election was held for the New South Wales Legislative Assembly electorate of Illawarra on 10 September 1866 following the resignation of Patrick Osborne.[1]
| Date | Event | |
|---|---|---|
| 24 August 1866 | Patrick Osborne resigned. | |
| 28 August 1860 | Writ of election issued by the Speaker of the Legislative Assembly.[2] | |
| 6 September 1866 | Nominations | |
| 10 September 1866 | Polling day | |
| 18 September 1866 | Return of writ |
John Stewart had been the unsuccessful candidate at the 1860 election, receiving 46.% of the vote,[3] and again at the 1864 election receiving 43.3% of the vote.[4]