The percentage of Catholics who say they are a “member” of a church has dropped by nearly 20 points since the year 2000, according to a new report by Gallup released on Monday.

Among respondents who said they were Catholic, only 58% actually said they were a member of a church. This figure is down 18 points from the 76% of Catholics who said they were a member of the Church, in a previous Gallup survey from 1998-2000.

In the past decade, Catholics saw a twice-as-steep decline in members than did Protestants, which saw a 9% decline in professed members of churches from 73% to 64%.

The report, based off a Gallup poll of more than 6,100 U.S. adults from 2018-2020, was published on Monday. Gallup says it asks Americans about their “religious attitudes and practices” twice per year.

In canon law, a baptized Catholic’s membership at a parish is conferred by territorial residence and not strictly by registration.

According to the report released on Monday, overall membership in houses of worship has continued its pre-existing decline in the U.S., reaching a record-low point of 47% in the survey conducted from 2018-2020. The figure is the lowest since Gallup began its survey in 1937, when 73% of Americans identified with a church or house of worship.

“The U.S. remains a religious nation, with more than seven in 10 affiliating with some type of organized religion,” Gallup stated. “However, far fewer, now less than half, have a formal membership with a specific house of worship.” While this could be due in part to the ongoing coronavirus pandemic, the report said, “continued decline in future decades seems inevitable.”

The report follows pre-existing trends of a rise in the “nones,” Americans who do not identify with any religion in particular, as well as decades-long declines in weekly church attendance.

Membership has declined with each successive generation. While 66% of “traditionalists” born before 1946 and 58% of baby boomers say they are members of a church, only 36% of millennials say they are a member of a church.  Nearly one-third (31%) of millennials say they do not belong to any religion in particular.

This decline in membership was even more pronounced among Hispanic Americans, among whom only 37% say they are a member of a church.

Church membership also declined more steeply among Democrats and residents of the Eastern U.S. than among political Republicans and Independents, and residents of other U.S. regions.