[1] McMillan attended Blair's grammar school in Fagg's Manor and studied theology at Robert Smith's Pequea Academy[2][3][4][5][6] He entered Princeton at 18 and graduated in 1772.

[1] Amid the Revolutionary War and attacks from local Indians, McMillan moved his wife and their first child to a cabin on Shanon Run, the east branch of Chartiers Creek in Washington County, Pennsylvania.

McMillan began teaching Greek and Latin to students in his log cabin, eventually graduating several prominent frontier ministers, including James McGready, William Swann, Samuel Porter, and Thomas Marquis.

[1] Gallatin's successor, James Ross was a classical teacher at McMillan's log college.

[1] McMillan served in the militia in Captain James Scott's Company of the Third Battalion of the Washington County Military.

[1] James Carnahan, President of Princeton University, said that he had aided church and education "more than any other man of his generation.