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