At least not in the USA. And not today anyway. See this cool article by Glenn Stanton…

http://thefederalist.com/2018/01/22/new-harvard-research-says-u-s-christianity-not-shrinking-growing-stronger/

He cites a paper by a researcher at Indiana University and Harvard…

https://www.sociologicalscience.com/download/vol-4/november/SocSci_v4_686to700.pdf

and his conclusions might startle you. Then again, maybe you never doubted. : ) (Thanks for the tip, Eric!)