Police said a member of the Islamic Center of Pflugerville discovered the vandalism after arriving about 6 a.m. Monday, reported KEYE-TV.
The incident is under investigation by police as a hate crime, and the mosque's members suspect the vandalism is a reprisal to last week's terrorist attacks by Islamic State militants in Paris.
"This is very unexpected and quite honestly, shocking," said Faisal Naeem, an ICP board member.
He worried that the mosque, which has rented space in the town outside Austin for about three years without incident, could become a target for violence.
"Can something like Wisconsin, the Sikh temple thing, happen here?" Naem wondered, referring to the fatal 2012 shooting of six worshipers by a white supremacist. "If you would have asked me this question yesterday I would have said, no, this is Austin -- but that is no longer true."
Investigators said vandals ripped apart a Koran, left it at the mosque's front door, and splattered fecal matter all over the entryway and what was left of the Islamic holy book.
Neighbors from various faiths stopped by the mosque after the vandalism was reported to show their support, and one 7-year-old boy emptied his piggy bank to donate $20 to the cleanup, which is expected to cost about $150.
“We were talking in the car how someone smeared poop on their church and that was a really, really awful thing to do and we had a good conversation what churches are for and how everybody’s churches are important,” said the boy's mother, Laura Swanson. “I think it’s really good to get kids involved and to let them know what the important stuff really is.”
Naeem, who has a son about the same age, said the donation greatly touched him and other members of the mosque.
“It’s 20 bucks, but coming from Jack collecting his pennies -- it’s worth 20 million bucks to me and to our community,” Naeem said. “This gives me hope because this means it’s not one versus the other.”
Vandals spray-painted a peace symbol incorporating the Eiffel Tower -- a design which has come to symbolize the Paris terrorist attacks -- on a mosque in Omaha, Nebraska.
Federal authorities are considering charges against a man who made threatening phone calls to two Florida mosques.
The man has been identified by investigators, although they did not release his name, but authorities dismissed the threats as not credible to "bomb (their) f*cking location" and shoot Muslims between the ages of 2 and 100 years old.
Muslim activists have asked the FBI to investigate that case as a possible hate crime.
Watch this video report posted online by KXAN-TV: