| Competition: | League of Ireland First Division |
| Season: | 2009 |
| Winners: | UCD |
| Promoted: | Sporting Fingal |
| Continentalcup1: | UEFA Europa League |
| Continentalcup1 Qualifiers: | Sporting Fingal |
| League Topscorer: | Conan Byrne 21 |
| Prevseason: | 2008 |
| Nextseason: | 2010 |
The 2009 League of Ireland First Division season was the 25th season of the League of Ireland First Division. The First Division was contested by 12 teams and UCD won the title. Third placed Sporting Fingal also won the 2009 FAI Cup Final, qualified for the 2010–11 UEFA Europa League and were promoted to the Premier Division after winning a promotion/relegation play off.
| Team | Base | Manager | Stadium | |
|---|---|---|---|---|
| Athlone |  Brendan Place | |||
| James Gallagher | ||||
| Joe Somerville | ||||
| Johnny Glynn | ||||
| UCD | ||||
| Stephen Henderson | ||||
This season saw the division expanded from 10 to 12 clubs. This was because the 2009 Premier Division was reduced to 10 clubs. The regular season began on 6 March and concluded on 7 November. Each team played the other teams three times, totaling 33 games. UCD finished as champions and were automatically promoted to the Premier Division. There was no promotion/relegation play-off between the First Division and the A Championship this season. This was only because Kildare County, who finished bottom of the table, withdrew from the League of Ireland before the play-offs could be played.[2] [3]
The second and third placed First Division teams, Shelbourne and Sporting Fingal played off to decide who would play the winner of the Premier Division play-off. The winner of this play off would play in the 2010 Premier Division.
| Scorer | Team | Goals | |
|---|---|---|---|
| Conan Byrne | Sporting Fingal[4] | 21 | |
| Karl Bermingham | Monaghan United | 17 | |
| Graham Cummins | Waterford United | 17 | |
| David McAllister | Shelbourne | 16 | |
| Ciarán Kilduff | UCD | 14 | |
| Stephen O'Flynn | Limerick F.C. | 14 |