You're hard pressed in this part of the country to keep a basement or crawl space dry without a sump pump. Newer houses will generally fare better (poured concrete wall, waterproof membrane, drainage plane w/drain tile and gravel, better grading, gutters, etc), but clay just holds so much water... sooner or later it'll get saturated and the water will find a way into the house.
I've done a lot of work to our house to try and keep the crawl space dry (it's basically on grade!), but it's to the point now where after a couple of hard rains, water seeps up from underneath. Burying drain pipes and installing a sump pump is the next step... but fawk trying to dig a ditch under the house.