Here are links to the homepages of various scholarly organizations.
The American Philological Association deals mainly with ancient Greece and Rome - language, literature, history, etc.
The Classical Association of the Atlantic States is the regional Classical association covering New York, New Jersey, Pennsylvania, Delaware, Maryland and the District of Columbia.
The Pennsylvania Classical Association serves the interests of the Classics in Pennsylvania.
The Linguistic Society of America deals with the scientific study of language.
The International Linguistic Association, based in New York City, likewise deals with the scientific study of language.
The American Oriental Society covers the ancient Near East, South Asia (Sanskrit, etc.), Islamic studies, China, Japan, Inner Asia, etc.
The Archaeological Institute of America deals with archaeology, especially Classical Mediterranean archaeology.