Middlesex won their first title, winning eight and losing one of their 18 games.
Yorkshire, the defending champions, finished third after losing five games.
Positions were decided on percentage of points over completed games.
Points system: Percy Clark and Bart King headed the wickets for the Philadelphians, who played 14 first-class matches in England, in addition to an abandoned fixture with Sussex.
In the batting, they were headed by captain John Lester, who made 786 runs in 13 matches.