Demetrius J. Atsalis (born March 31, 1964, in Hyannis, Massachusetts) is a Democratic Party politician who represented the 2nd Barnstable District in the Massachusetts House of Representatives from 1999 to 2013.

His district included precincts in Barnstable and Yarmouth, Massachusetts including lands proposed by the Mashpee band of the Wampanoag people to be set aside in federal trust for the purposes of Indian gaming.

Atsalis is a proponent of plans by Mashpee Chairman Cedric Cromwell to develop a broad scale Native American reservation casino resort complex[2] to be financed by the Genting Group in his district.

[4] A graduate from Barnstable High School, he earned a social studies certificate from Salem State University and a B.A.

[5] Before his election he served on the Hyannis Civil Executive Board and the Hyannis Waterfront Action Group and was involved with Barnstable youth baseball and soccer.