The concept has it's origin in Pat Bidol's "Developing New Perspectives on Race" from 1970 and was largely popularises by Judy H. Katz, who referred to Bidol's "Racism = Prejudice + Power" concept in her book "White Awareness" in 1978. This book presented a course of counter-racist training for organisations.

That said, Bidol was not the first one who spoke of institutionalised/structural racism. In 1967 Stokely Carmichael and Charles V. Hamilton already used the term institutionalised racism in their book "Black Power".

Sources:

Pat Bidol: Developing New Perspectives on Race. An Innovative Multi-media Social Studies Curriculum in Race Relations for the Secondary Level, New Detroid, 1970 Judy H. Katz: White Awareness: Handbook for Anti-racism Training, University of Oklahoma, 1978 Stokely Carmichael and Charles V. Hamilton: Black Power: The Politics of Liberation. Vintage Books: New York, 1967