The articles made me curious about church membership in the US (2002 census):
Catholic (Roman)            63 million
Southern Baptist            15 million
United Methodist             8.3 million
Church of God in Christ      5.4 million
Latter Day Saints (Mormon)   5.2 million
Evangelical Lutheran         5.1 million
National Baptist             3.5 million
Presbyterian                3.5 million
Assemblies of God            2.6 million
Lutheran-Missouri Synod      2.5 million
Prog. Nat. Baptist          2.5 million
African Methodist            2.5 million
Missionary Baptist          2.5 million
Episcopal                   2.3 million
Greek Orthodox               1.3 million
and many others

Haven't found figures for non-Christians yet