Like Nurse Joy, there are many Jennies who are all related and look/sound exactly alike. They enforce the law all throughout the Pokemon world.
And also like Joy, some are different but most share common traits.
Police Pokemon are Growlithe, which some Jenny train to round up criminals. Jenny is always concerned about people breaking the law, and shows no sign of being a corrupt cop. She is responsible, take-charge, strong, gutsy and kind, helping Ash out - although they help her out often too. Some ride motorbikes, some boats and some cars.
Some different Jennies are the one at Neon Town, who was crabby and irritable due to lack of sleep. Pinken Island Jenny was there to care for the Pokemon and ensure that no poachers came to disturb them. The identical officers, unlike Joys, do not have quite so much diversity; all of them enforce the law in some way.
Jennies may patrol areas of frequent crime, some protect things, some break up fights, some apprehend criminals and some investigate crimes.
Brock got crushes on all Jennies (as well as all Joys). Tracey seems to like them too.
Orange League Jennies have a slightly different uniform.
Jenny's voice sample - click here to hear what she sounds like. "Well, you look like you really didn't know, so I'm going to let you go with a warning this time." (Boy, no wonder the world of order is in shambles! Wouldn't it be great if normal cops did that? ^_^;;)
--Jenny pic from Pokemon Picture Archive--
