Philadelphia ? Even as financially strapped Catholic schools continue to close across the country, no one in Philadelphia ever thought the church would shutter Cardinal Dougherty High School.

Not the flagship campus that once boasted 6,000 students and billed itself as the biggest Catholic school in the world. Not the school whose marching band once played for a pope, a princess and a presidential inauguration.

Not Cardinal Dougherty.

But the unthinkable came to pass in October when the Philadelphia archdiocese announced 2009-10 would be Dougherty’s last school year. The school, a victim of declining enrollment and changing demographics, will close this month after 54 years and more than 40,000 graduates.

“My head understands it, but it really hurts your heart,” said 1966 alumnus Tony Conti. “This is where I went to high school, this is where I met my wife.”

Dougherty is hardly alone. Nationwide, 174 Catholic schools have closed in the past year, compared with 24 opening, according to the National Catholic Education Association. Catholic school enrollment in the U.S. has declined 20 percent in the past decade.

Named after a former archbishop of Philadelphia, Dougherty opened in 1956 in the city’s East Oak Lane section with more than 2,600 freshmen and sophomores.

The students — nearly all white and nearly all Catholic — paid no tuition, because local parishes could afford to subsidize the cost. A wall divided the boys’ and girls’ sides of the building.

Urban Catholic schools have been hard hit by dwindling enrollment. Neighborhoods once filled with large families have emptied as parishioners move to the suburbs. For those in the city, free charter schools are an appealing option.

Some dioceses paying settlements to priest-abuse victims have less money to subsidize school operations. Fewer subsidies leads to higher tuition, which fewer families can afford in a recession, creating a vicious circle.