Where to Find and Catch Terrakion
From Pokemon Go Wiki
Terrakion are found and captured in Nest and Habitat locations.
Nests
Terrakion Nests are locations that consistently spawn Terrakion.
Habitats
Terrakion Habitats are spawn locations where Terrakion 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: