| Competition: | III liga |
| Season: | 2020–21 |
| Winners: | Pogoń Grodzisk Mazowiecki Radunia Stężyca Ruch Chorzów Wisła Puławy |
| League Topscorer: | Krzysztof Bartoszak (29 goals)[1] |
| Prevseason: | 2019–20 |
| Nextseason: | 2021–22 |
The 2020–21 III liga was the 13th season of the fourth tier domestic division in the Polish football league system since its establishment in 2008 under its current title (III liga) and the 5th season under its current league division format.
The competition was contested by 84 clubs split geographically across 4 groups, with the winners of each group gaining promotion to the II liga. The season was played in a round-robin tournament. It began in August 2020 and ended in June 2021. The teams included semi-professional clubs (although a few are professional) and the reserve teams of professional clubs.
From October 17, 2020, due to the COVID-19 pandemic restrictions, all III liga football matches take place behind closed doors without any spectators.[2]
84 teams are divided into four groups according to geographical criteria:
Each group of III liga is managed by a different voivodship football association. In the 2020–21 season these are the following regionals federations:
The following teams have changed division since the 2019–20 season.
| Competition: | III liga Group 1 |
| Season: | 2020–21 |
| Winners: | Pogoń Grodzisk Mazowiecki |
| League Topscorer: | Bartosz Giełażyn Kamil Zalewski (27 goals each)[3] |
| Competition: | III liga Group 2 |
| Season: | 2020–21 |
| Winners: | Radunia Stężyca |
| League Topscorer: | Krzysztof Bartoszak (29 goals) |
| Competition: | III liga Group 3 |
| Season: | 2020–21 |
| Winners: | Ruch Chorzów |
| League Topscorer: | Marcin Przybylski Piotr Stępień (25 goals each)[4] |
| Competition: | III liga Group 4 |
| Season: | 2020–21 |
| Winners: | Wisła Puławy |
| League Topscorer: | Adrian Paluchowski (28 goals)[5] |