On June 13, 1863, when Lee's Second Corps shattered the Union Milroy's division at Winchester, breaking through the Federal front and advanced towards the Maryland and Pennsylvania, followed by the First and Third Corps, which within June 24 crossed over the Potomac at Williamsport marching through the Maryland directed to Pennsylvania.
The only time that the South invaded the North was at Gettysburg, PA, in 1863.
Gettysburg
Meade tuned back Lee's invasion of the North. Lee never invaded the North again.
In the summer of 1863, Lee fought the Battle of Gettysburg on 1-3 July
To deny Lee the psychological triumph of having invaded the North. Also, in the run-up to the battle, to keep Lee occupied, so that he could not send troops West to help at the siege of Vicksburg.
The battle took place in the city of Antietam.
The North was fairly untouched by the war. Lee invaded Maryland in 1862 and Pennsylvania in 1863. There were some incursions into Kentucky, and a few cavalry raids into Indiana and Ohio, and there was an attack by saboteurs in Vermont (of all places) but nowhere near the number of actions in the South.
Robert E. Lee
Robert E. Lee.
Lee led two invasion of the North. One led to Antietam in 1862. The other led to Gettysburg in 1863.
Meade saved the Union from Lee's invasion and Lee never invaded he North again.
When Lee retreated back to Virginian, he never again invaded the North.