Sir Stephen Theodore Janssen, 4th Baronet (died 7 April 1777) was an English Member of Parliament and Lord Mayor of London.
[1] He was the 4th son of Sir Theodore Janssen, 1st Baronet and the younger brother of Sir Abraham Janssen, 2nd Baronet.
He succeeded his other elder brother Sir Henry Janssen, 3rd Baronet to the baronetcy in 1766.
In 1749 he was appointed one of the Trustees for the Establishment of the Colony of Georgia in America.
Henrietta married Lorenzo Moore (MP for Dungannon).