St. John’s University will move its graduate center to Hauppauge in June, leasing a new, modern location after selling its waterfront mansion and 170-acre campus in Oakdale for $22.5 million last September, university officials announced Thursday.

The Queens-based Catholic school signed a five-year lease on a one-story building in an office park at 120 Commerce Dr.

St. John’s, which has a total undergraduate and graduate enrollment of more than 21,000, has offered graduate courses through its School of Education at its Oakdale site since 1999.

About 300 students currently are taking courses there, and the university projects that more than 400 students will enroll in the fall semester, officials said. The school also has campuses in Manhattan, Staten Island and Rome, Italy.

“We are committed to continuing to provide quality graduate education programs on Long Island,” St. John’s University Provost Robert A. Mangione said in a statement. “This new, centralized location provides us with the opportunity to serve our current students and to expand the academic offerings at this site.”

University officials said the new Long Island Graduate Center will feature six state-of-the-art classrooms, video-equipped conference rooms that will allow for an interactive learning experience, offices for full-time faculty based on-site, student gathering spaces and space for special events.

advertisement | advertise on newsday

St. John’s officials said the university has requested approval from its accrediting agency, the Middle States Commission on Higher Education.

Courses currently under way in Oakdale will continue as planned. The university said it will move all of its Long Island operations to Hauppauge after the spring semester.

St. John’s has offered graduate education courses on Long Island since the school in 1999 purchased the property at 500 Montauk Hwy. in Oakdale for $14.3 million from the LaSalle Christian Brothers, who operated LaSalle Military Academy there for more than 75 years.

The site was the estate of Frederick Bourne, president of Singer Sewing Machine Co., from 1889 to 1905. The main structure on the campus, the Bourne Mansion, was built in the Georgian architecture style in 1897 and has sweeping views of Great South Bay.

The property was sold in September to Amity Education Group, which operates Amity University, one of the largest multi-campus colleges in India, which said it planned to open a school for international students.