On his first day as parks director of a county with one of the region’s largest Jewish populations, Mike Riley received an e-mail that would prove stressful: His department had apparently scheduled the annual Harvest Festival — one of its biggest events — on the same day as Yom Kippur, the holiest day on the Jewish calendar.

Holding the festival, which draws about 4,000 people to activities such as sheepdog demonstrations and country music performances, on a day when the vast majority of Jews can’t come is insensitive, read the e-mail from a Jewish volunteer to the Montgomery County official. Yom Kippur is Oct. 4 this year.

Riley had received just that one e-mail, and his staff said the same conflict had happened several years ago — and the festival had gone ahead anyway.

This time, marketing for the event hadn’t begun and only people involved even knew about the date. The new director, who oversees 421 parks in the county, spoke to some of his Jewish colleagues and other department leaders and “their reaction was totally universal: ‘Oh my gosh,’” he recalled.

After trying unsuccessfully to reschedule the festival, Riley announced Wednesday he was canceling the 24-year-old event for 2014, setting off dozens of angry e-mails and making clear the tightrope officials walk when it comes to religious sensitivity in fast-changing Montgomery.

“I am absolutely disgusted with Mr. Riley’s poor decision making and leadership,” Rex Reed, president of the Friends of the Agricultural History Farm Park, which was to host the festival, wrote to his constituents Thursday. He noted that the festival a few years ago switched to include Saturdays, the Jewish Sabbath, which means Orthodox Jews wouldn’t be able to go anyway since many don’t drive that day. “Apparently, it is OK to discriminate against some Jews, but not others,” Reed wrote.

“In this country we have the freedom to practice our different religious beliefs, and we are all free to make our own decisions as to what we attend,” the letter read.

Montgomery’s Jewish community is large and well established, but rapid immigration in the past 15 years has raised the profile of other religious minorities, particularly Muslims and Hindus. Muslims and other advocates have been pressing for public schools to be closed on at least one of two major Muslim holidays, or at the minimum for the holidays to be noted on the school calendar along with Jewish ones.

Riley said he feels bad about canceling the event, which brings the county about $10,000 in admission and parking fees and involves hundreds of volunteers and staff and vendors.

Some e-mails, he said, “have been kind of nasty,” saying he was showing disrespect for the nonprofit agriculture-related groups who display there and for vendors who sell items such as food, knitted products and plants.

The Parks Department, he said, had been working to hire an outreach coordinator to respond to Montgomery’s growing diversity and to “get a wider range of input” — in particular from its expanding Latino population. “We tend to get a lot of long-standing civic people giving input; sometimes we use the term ‘usual suspects.’ ”

But being “religiously sensitive” isn’t simple when you’re a huge suburban county government.

In denying Muslim residents school cancellations, school officials said past decisions to close for Jewish and Christian holidays have been based on student and staff absenteeism, not to commemorate a religious event. But advocates say the district never defined what level of absenteeism was present when other holidays were established, nor what would be the required level now.

“That decision is murky in its history. No one knows the reason, no matter what is said,” George Leventhal, an at-large County Council member, said of how Montgomery decades ago decided to cancel school on the first day of Rosh Hashanah and on Yom Kippur, two key Jewish holidays that come in the fall. Leventhal, an advocate of getting Muslim holidays recognized, said he sees many new residents from Pakistan, Egypt, Libya and Somalia, among other places with large Muslim populations.

Regardless, Leventhal said he agreed with Riley’s decision.

“Especially to have a public event celebrating food on a fast day — that would appear boneheaded, and insensitive,” he said.

It has been deemed unconstitutional for the government to seek information about religion, so annual official data on Montgomery’s faith makeup — and change — doesn’t exist. However, a privately funded survey of the region in 2003 found that 41 percent of the region’s 215,600 Jews live in lower Montgomery County.

Montgomery’s Jewish population is visible in public life, from the many Jewish officials to multiple Orthodox synagogues and schools around the Kemp Mill area. Experts agree that Jews are far from the majority in the very diverse county, with churches on every other corner and prominent faith institutions including a temple of the Church of Jesus Christ of Latter-day Saints in Kensington and the headquarters of the Seventh-day Adventist Church in Silver Spring.

The county’s racial minority population rose 40 percent between 2000 and 2010.

Artist Phillip Ratner said he and his family opened a museum focused on Old Testament art in Montgomery in part because he lived there but also because of the large Jewish population. He said he wouldn’t take it as an affront if a private group held an event on a Jewish holiday.

If it were a large, private organization “that just had like 10 percent Jewish [members or customers], so you don’t cancel! The Jews don’t go! You don’t have to affect the whole world around you,” he said.

But the county shouldn’t discriminate. “That’s different,” Ratner said. “We don’t need any wars.”

Riley said the Parks Department staff who set the festival had simply followed tradition, as the event is always held on the first weekend in October. They saw the conflict, but “failed to elevate the issue,” he said. “This is a new experience for me. It’s been eye-opening.”