There's an extensive discussion of the historical background here but I'll try to summarize.
Between 1775 and March 1777 the PA militia were only semi-official, due to the pacifist ideals of the Quaker founders. In March 1777 the militia became official, so the table of organization I relied upon for the first paragraph reflects the initial establishment. This lasted for 3 years, with a new establishment in 1780, when Rippey, Reed, and McNarry were not re-elected as Captains.
Each member of militia could be called up for 2 months of active duty at a time, therefore they were divided into "classes" with all members of the class being called,. A call-up would find neighbors still serving together, but their colonel would be different and their battalion designation would be different. (Read the historical background for an explanation.)
When and where was Captain John on active duty? Can't tell at the moment, Here's what the historical background says:
Most of the service rendered by members of the Pennsylvania Militia fell into one of three categories. They were either used to augment the operations of the Continental Line such as when some of the Associators accompanied General Washington in crossing the Delaware in January 1777. Other examples of this type of service include the large numbers of Pennsylvania militia employed in the summer and autumn of 1777 to oppose the British invasion at Brandywine and on the flanks at the battle of Germantown, though in neither case did they actually see action. The militia did provide a significant defensive force patrolling the south side of the Schuylkill River and engaged in occasional clashes with British outposts and scouting parties including heavy skirmishes at Whitemarsh on December 7. Due to the sixty-day turnover, however, none of the men who were at Brandywine in September would have been present at Whitemarsh in December. It is known that no Pennsylvania militia served at Valley Forge, Monmouth, or Yorktown. The second type of service was duty on the frontier in Northumberland, Northampton, Bedford and Westmoreland counties. Occasionally, militia reinforcements from Cumberland, Lancaster, and York counties would be brought in to reinforce these frontiers as occurred in the summer of 1778. A third type of militia duty was in providing guards for supply depots located in Lancaster, Lebanon and Reading and at various prisoner of war camps.