There are many, many registries available. Most states have them but they are not perfect by any means. For example: To use them effectively, you first have to know the correct state where the birth and the adoption occurred. It is not uncommon for these two events to have occurred in two different states and for many searchers, this basic information is often lacking. In addition, in order to work, all the registries depend on both the birthmother and/or birthfather and the adult adoptee to first register with them. While their success rate is not high, registering does remain an important step for someone who is seriously searching.
The largest and most important registry is the International Soundex Reunion Registry (ISRR).
ISRR is a nonprofit, humanitarian agency which serves and promotes, through the reunion registry, the interests of adults desiring and seeking a reunion with next-of-kin by birth. The Registry serves the needs of birth family members who have been separated by adoption, divorce, foster care, institutional care or abandonment. ISRR is not affiliated with any registry or other organization. ISRR is the largest free search registry in the world. This registry does not perform a search or provide search advice. Voluntary registration by adults desiring contact or reunion with their next of kin by birth is deemed legal consent for contact.
If you are going to register anywhere – register with the ISRR.