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