Gallup reports:

From 2014 to 2017, an average of 39% of Catholics reported attending church in the past seven days. This is down from an average of 45% from 2005 to 2008 and represents a steep decline from 75% in 1955. By contrast, the 45% of Protestants who reported attending church weekly from 2014 to 2017 is essentially unchanged from a decade ago and is largely consistent with the long-term trend.

As Gallup first reported in 2009, the steepest decline in church attendance among U.S. Catholics occurred between the 1950s and 1970s, when the percentage saying they had attended church in the past seven days fell by more than 20 percentage points. It then fell an average of four points per decade through the mid-1990s before stabilizing in the mid-2000s. Since then, the downward trend has resumed, with the percentage attending in the past week falling another six points in the past decade.