Occasionally militia units were sent outside their Counties to join a Continental campaign.This was very rare and exceptional, usually in an emergency.This did not change the Militia status as a County organization although their command was *temporarily* tactically under the campaign command.Neither did this make the Continental and/or State Troops that were involved in the same action part of the Militia (Militia officers never commanded State or Continental troops).After the action was over each military organization retained its own essential structure and basis for existence, even when significant numbers were captured by the British.
This should not be confused with recruiters for the Continentals enlisting men for 9 months or a year, especially early in the War.Such men became part of the Regiment into which they'd been recruited and were not part of their local home Militia until they were discharged at the end of their enlistment terms.
Occasionally County Militia were the only responders to British incursions, such as in the Mohawk Valley and on the western frontier of PA/Virginia.They retained their County Militia status.
At times parts of Militia units were drafted into or incorporated into the Continentals (viz. the complicated history of the MD and VA Rifle Regiment).They ceased being Militiamen and became members of Continental Regiments.
By and large most County Militia never saw active duty.