Whether or not adoption records are open or closed is going to vary based on the type of adoption that is selected. Adoption Help.org indicates that open adoption has "become the norm in the U.S. for infant adoptions." This means that if you are adopting a child today, there is a good chance the adoption will be an open one. However, this doesn't have to be the case, and if you were adopted or adopted a child in the past, there's a good chance that your adoption would not have been open.

In a closed adoption, either no information or very little information would generally be made available to the adoptive parents or child about the birth parents. There would not have been ongoing or continued contact and in most cases, birth and adoption records would have been sealed. This meant sealed records usually couldn't be accessed at all, except potentially in a very, very small array of exceptions.
The idea of the closed adoption dates back to the 1900s and closed adoptions were especially popular during the 1950s to the 1970s. During this time, if you gave a child up for adoption, there was often a strong element of shame involved. An out of wedlock pregnancy, for example, could be disastrous to a reputation. This often meant if you were giving a child up for adoption, you would not want others to know. Many early adoption laws actually prohibited the sharing of information about the individuals involved in the adoption, such as the child’s birth parents or other information. For many years, this was the standard by which adoptions took place and were handled.
For a period of time, birth records could actually be altered and new birth certificates produced to include the name of the adoptive parents. This meant an adopted child might not have even been able to find an original birth record even if it was not sealed or if the record was unsealed, because it may have been modified as a part of the adoption process.
Complicating matters still further, in early adoptions, names were often not put on birth certificates in cases of illegitimate births, because of the shame associated with it.
Things began to change around the 1980s and 1990s. Today, the adoption process tends to be much more open, and children are often able to know who their birth parents are and to maintain contact with them. This is the case in roughly 80% of adoptions that take place today, according to Adoption Help.org.
An open adoption can be as open as the parents want it to be within the bounds of state law. For example, an open adoption may be limited to knowing basic information about the birth parents and their medical history.
Open adoptions can also involve regular, continuing, ongoing contact. Sometimes adoptive parents simply send pictures and updates to birth parents, but in other cases the child actually gets to develop a relationship with and visit the birth parents periodically.
Open adoption can allow an adopted child to know more about his background, family and medical history. They can also create a more comfortable arrangement for some birth parents who don't want to cut all ties with their babies.
In some cases, families or mothers may decide that open adoption is not right for them. In such cases, it may be possible for a closed adoption to be arranged depending on state law.