IN THE UNITED STATES
According to Wikipedia (“Catholic Church in the United States“):
There are 68,503,456 registered Catholics in the United States (22% of the US population) according to the American Bishops’ count in their Official Catholic Directory 2010.
As for the Orthodox, the Orthodox Church in America says:
It would be safe to say that there are somewhere between 2 and 3 million Orthodox Christians in North America in roughly 2,000 parishes.
IN THE WORLD
Worldwide, Wikipedia (“List of Christian denominations by number of members“) reports about 1.2 billion Catholics, 600-800 million Protestants, 230 million Eastern Orthodox, 82 million Oriental Orthodox, and some other minor divisions. (Eastern Orthodoxy and Oriental Orthodoxy are distinguished in this Wikipedia article: “Orthodox Christianity.”)
As for the Orthodox in the world, Wikipedia (“Eastern Orthodox Church“), says:
Based on the numbers of adherents, Orthodoxy is the second largest Christian communion in the world after the Roman Catholic Church. The most common estimates of the number of Orthodox Christians worldwide is approximately 225–300 million. The numerous Protestant groups in the world, if taken all together, outnumber the Orthodox, but they differ theologically and do not form a single communion.
Nonetheless, Church Is Not the Answer; Christ Is.