During the gilded age the US population rose from what to what?

During the gilded age the US population rose from nearly 40 million in 1870 to nearly 80 million in 1900.

The answer to your question is that during the gilded age the US population rose from nearly 40 million in 1870 to nearly 80 million in 1900. The population increased because of industrialization and the modern technologies that US has.