An 18-year-old Barnard freshman was fatally stabbed just after nightfall on Wednesday during a mugging in a park near the college’s Manhattan campus, the police and college officials said.

In a campuswide letter sent around 11 p.m., Sian Leah Beilock, Barnard’s president, identified the victim as Tessa Majors and said she had been killed in an armed robbery in Morningside Park.

“Tessa was just beginning her journey at Barnard and in life,” Ms. Beilock wrote. “We mourn this devastating murder of an extraordinary young woman and member of our community.”

Ms. Beilock said in the letter that she and Leslie Grinage, the dean of the college, had spoken with Ms. Majors’s parents, who were on their way to New York. She also urged “anyone in need” to take advantage of the college’s counseling services.