It is happening, but it is not too late to turn it around. This site below is full of factual data that breaks down the statistics of the decline:
FACT: Statistics on Religion in America Report -- Pew Forum on Religion & Public Life
More important the site below this paragraph is research based information as to WHY this trend is ongoing.
REASON WHY: Why Is Christianity on the Decline in America? – The Gospel Coalition Blog
Knowing and accepting that it is happening is knowledge. Knowing why is the first step to change our attitude in an effort to reverse the trend. Many actions theists are taking to increase Christianity is the cause of its decline.
Anyway, I am on a quest for knowledge and found these two sites interesting.