Diamond Credit Union. 1600 Medical Drive, Pottstown, Pa 19464. Earning Your Trust One Dollar at a Time. The largest full-service credit union serving Berks County and the Tri-County Region. Pottstown Branch: 610-326-5490. Reading Branch: 610-396-9980. Toll-free: 800-593-1000. Website: www.diamondcu.org. Your savings federally insured to at least $250,000 and backed by the full faith and credit of the United States Government by the National Credit Union Administration, a U.S. Government Agency.