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