PORTSMOUTH — Seacoast religious leaders said a recent cultural shift toward secularism has caused them to make significant changes, including altering their strategy for attracting members and consolidating churches.

Secularism, which experts say has always been prevalent in New Hampshire and has continued to rise, has caused attendance to dwindle in many religious congregations. A Gallup poll in 2015 stated 20 percent of New Hampshire was considered “very religious,” the lowest percentage found in the poll. Mississippi came in at the highest with 63 percent.

In Portsmouth, Corpus Christi Parish, which is comprised of St. James Church, St. Catherine of Siena Church and the Immaculate Conception Church, is being consolidated into one church, and St. James Church is being put up for sale.

Father Gary Belliveau, who leads the parish, said there is no longer a need for three churches led by three different priests.

Belliveau said Catholicism was more prevalent in Portsmouth in the 1980s, but church attendance began to decrease in the late 1990s, leading to the three churches joining under one parish in 2006. Shifts in the city’s demographics played a part in this, he said, but secularism was a factor.

“What I think we’re facing today with secularism is basically, there’s been the shift from a reliance upon God and a deeper appreciation for the things beyond what we can see and figure out, to the reliance on self,” Belliveau said.

Dover’s St. Charles Church was torn down last month and the site is expected to be used for workforce housing.

Tom Bebbington, director of communications for the archdiocese in Manchester, said changes in demographics were a factor in the diminishing need for St. Charles Church, as well as the building’s poor condition. However, he said secularism has played a part in that need going away as well.

Michele Dillon, a sociology professor at the University of New Hampshire who specializes in religion, said New England states have experienced a drop in religious participation at an accelerated rate compared to other parts of the country.

Pastor Ken Lawrence of the Hampton Falls First Baptist Church said his church has continued to do well, but that has been the result of hard work in adapting the church’s approach to evangelism.

For example, he said, conversations with nonbelievers today need to begin with establishing the Bible as an authoritative book, where before the strategy might be to start with what Jesus says in the Bible.

“It affects our starting point,” Lawrence said. “Where it used to be assumed there was a god, now we have to do a pretty good job of establishing the basis of authority in the Bible. (We need to answer) why is the Bible the authority before we can talk about using Bible verses. And if churches don’t do that, if we don’t do that, then shame on us.”

For some churches that have continued to thrive, growth has come as a result of churchgoers traveling from surrounding towns that once had more active churches. Belliveau said his parish draws families from communities including Strafford, Greenland, Newington, Newfields and towns in Maine.

“A few churches thrive and for whatever reason they get critical mass, and churches in smaller towns sort of dwindle away,” said Reverend Emily Heath, who leads the Congregational Church in Exeter. “What you see is church mergers or churches shutting down. There used to be a church in every town in New Hampshire.”

Some are skeptical of the data presented by studies such as the recent Gallup poll.

Rabbi David Senter of Temple Israel in Portsmouth said it is difficult to gauge the trends of religious communities because there are many intangibles that factor into why certain generations or regions choose to associate with a religion.

He said there was also a decrease in religiosity after World War II and that many members of the Greatest Generation who abandoned their faith eventually went back to religion.

Senter believes people in their 20s or 30s could possibly become more religious later in life, as people today tend to start families later than in past decades. Family life tends to draw people to religion, he said, as do other life events like the death of a family member or an experience with illness.

Professor Dillon said millennials may not turn to religion as they get older, though. She said more young people have already grown up in families that moved away from religion.

Reverend Patricia Marsden of the Newmarket Community Church believes the recent decline in religiousness is not a death knell. In the case of Christianity, she said, the church has historically gone through significant changes about every 500 years with major events like the birth of Jesus, the Crusades and the evolution of monasticism, a religious way of life in which worldly pursuits are renounced to devote oneself fully to spiritual work.

“We’re in that now. We’re in the 500-year phase,” Marsden said. “I believe church, God, isn’t going anywhere, but our churches are changing, and we need to change.”

Religious leaders also said they have seen people attending church who are more dedicated to their faith than in years past when more families attended church as an obligation.

Belliveau said his church has many young people who are coming on their own and appear to genuinely believe their faith is important. That makes him optimistic.

“We’re swimming against the current,” he said. “To swim against the current, you need to be strong. I think in a way we’re experience a deepening of fervor, zeal.”

Some Granite Staters find an unrestricted spiritual experience to be more palatable than conventional religions. Reverend Chris Jablonski, a minister at the Universalist Unitarian Church in Portsmouth, said his church has grown from about 325 members to more than 475 since he arrived at the church six years ago.

Unitarians do not worship a specific deity but instead pursue spiritual growth without boundaries. In years past, Jablonski said it was more common to find people leaving other faiths for Unitarianism, but he said new members today typically come from no spiritual background and are starting with South Church.

The congregation includes both theists and atheists, and services are based on original story telling that speaks to the church’s values.

While experts say religion is on a downward trend both locally and nationally, Jablonski said seacoast residents have a diverse array of options for worship.

The Islamic Society of the Seacoast Area, now located in Dover, is in the process of seeking approval from the city of Portsmouth to build a new place of assembly on Maplewood Avenue. A representative of the Islamic Society could not be reached for comment for this story.

“I think whatever you’re hungry for, there’s something there for you in the seacoast,” said Jablonski.