I was born in Chester County, PA— I grew up in Oxford, PA, which is about the greatest place on the planet for horses.
I moved away for many year, living in several different southern states. A few years ago I came back north, this time in Maryland.
Most of the greater Philadelphia area is very good for horses in the sense we have a lot of access to riding, quality barns, and services no matter where you live. The tough part is there is a lot of urban sprawl.
In the towns immediately around the city, much of the horse-keeping land has been lost to houses. There are still a fair number barns considering how built up it is, but they are pricey and traffic congestion will be heavy enough to limit your options. There aren’t going to be many options to keep your horses at home.
In the areas that still have a lot of farms and open land, you’re looking at a pretty substantial commute to the city and the Philadelphia airport. Though it may not appear far away on a map, traffic is going to be quite heavy in and around the airport during daytime/commuting hours.
If your husband’s trips will be infrequent or at odd hours, the world is your oyster. Chester County is a fabulous option, but you can pretty much go any direction and find a good horse community.