There were 363 clubs competing in Tercera División (Third division) in the 2008–09 season, divided into 18 regional groups, each accommodating between 20 and 21 clubs.
The following clubs finished as champions of their respective groups
The 18 group champion clubs participated in the Group winners promotion play-off and the losers from these 9 play-off ties then proceeded to the Non-champions promotion play-off with clubs finishing second, third and fourth.
^Soledad resigned from Tercera División at the end of the season and thus relegated to Preferente, so Arenal was re-admitted to Tercera División.
^Due to relegation to SE Eivissa-Ibiza from Segunda División B to this group, the reserve team, SE Eivissa-Ibiza B, was forced to relegate to Preferente.
^Cala d'Or resigned from Tercera División at the end of the season and thus relegated to Preferente, so Mercadal was re-admitted to Tercera División.
^Moratalla promoted to Segunda División B due to Lorca Deportiva CF administrative relegation to Tercera División.
^Due to relegation to Lorca Deportiva CF from Segunda División B to this group, the reserve team, Lorca Deportiva CF B, was forced to relegate to Preferente.
^2 points deducted for not paying three times the referee rights.