Where to Find and Catch Foongus
From Pokemon Go Wiki
Foongus are found and captured in Nest and Habitat locations.
Nests
Foongus Nests are locations that consistently spawn Foongus.
Habitats
Foongus Habitats are spawn locations where Foongus is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: