Sadness at his death was expressed by his school on Twitter.
Sinn Fein MLA Declan Kearney said Mr Lagan was a “highly respected principal”.
“I was shocked and very saddened to learn about the death of a motorist after a tree fell on his car while travelling along the Dublin Road in Antrim town on Friday evening,” he said.
“The victim of this tragedy, Francis Lagan, was a highly respected South Derry school principal, who made an immense contribution to the community which he served. Francis was a renowned Maghera educationalist and civic leader.
“My thoughts and sympathies are with his family, school colleagues and students, and the wider community of Maghera, where he was held in very great regard.”