The US of A.
Yes, most of them are Christians.
Poland
Bulgaria
Jordan
Brazil has many christians as it is a christian country , and most are catholics.
egypt
In the U.S., 79% In the world, about 33%
Probably either India or the Philippines.
I assume you mean sub-saharan africa- and in that case it would be South Africa (the country).
The most popular religion in South Africa is Christianity (68% of the country are Christians)
South Africa has the most Christians. They practice this religion 4 times per week.
The country with the most Christians on earth, at the present time, is China, estimates are around 60 to 75 million. It is only an estimate because many Christians in China attend "underground" or non-government approved churches.