When citing GeoPandas, you can use Zenodo DOI for each release. Below is the example of resulting BiBTeX record for GeoPandas 0.8.1 and a reference using APA 6th ed.

Kelsey Jordahl, Joris Van den Bossche, Martin Fleischmann, Jacob Wasserman, James McBride, Jeffrey Gerard, … François Leblanc. (2020, July 15). geopandas/geopandas: v0.8.1 (Version v0.8.1). Zenodo.

  author       = {Kelsey Jordahl and
                  Joris Van den Bossche and
                  Martin Fleischmann and
                  Jacob Wasserman and
                  James McBride and
                  Jeffrey Gerard and
                  Jeff Tratner and
                  Matthew Perry and
                  Adrian Garcia Badaracco and
                  Carson Farmer and
                  Geir Arne Hjelle and
                  Alan D. Snow and
                  Micah Cochran and
                  Sean Gillies and
                  Lucas Culbertson and
                  Matt Bartos and
                  Nick Eubank and
                  maxalbert and
                  Aleksey Bilogur and
                  Sergio Rey and
                  Christopher Ren and
                  Dani Arribas-Bel and
                  Leah Wasser and
                  Levi John Wolf and
                  Martin Journois and
                  Joshua Wilson and
                  Adam Greenhall and
                  Chris Holdgraf and
                  Filipe and
                  François Leblanc},
  title        = {geopandas/geopandas: v0.8.1},
  month        = jul,
  year         = 2020,
  publisher    = {Zenodo},
  version      = {v0.8.1},
  doi          = {10.5281/zenodo.3946761},
  url          = {}