Has a tornado ever happened in Northern Erie county?

If you mean Erie County, Pennsylvania then yes.

Since 1950 there have been 7 confirmed tornadoes in northern Erie County, PA.

The most significant of these was an F2 that touched down north of Lake City on September 18, 1977, injuring 7.

The most recent was a brief EF0 that touched down in Presque Isle State Park on June 27, 2010.