There are a fair number of websites that claim to provide useful information on horse riding trails. Unfortunately many of them are focused on big trails out west or dominated by mountain biking and hiking info. Others require you to sign up before you can access any useful info! That’s a crock.
This site will hold a few guides created to encourage horseback riding and horse driving use of trails and parks in Pennsylvania and maybe Maryland or New York. All are based as much as possible on personal experience, and try to include accurate (as of 2022) and comprehensive information, unlike most sites.