Marilyn Sue O’Hara

1960 - 2018

Marilyn Sue O’Hara, also known as Marilyn Ruiz, died September 30, 2018, following a collision between her car and a semi-truck at an intersection near her home in Urbana-Champaign, Illinois. She was 58 years old. She is survived by her parents, four children, and six siblings.

Marilyn received her Ph.D. in Geography at University of Florida in 1995. Her dissertation was titled  “A Model of Error Propagation From Digital Elevation Models To Viewsheds.” Her dissertation advisor was Grant Ian Thrall. Her Bachelors and Masters degrees were from University of Illinois. Her selection of UF for her doctorate degree came about because of communications with Grant about Spatial Diffusion, Grant at  the time was resident scholar at the Homer Hoyt Institute, doing research on spatial diffusion of urban development, and he had recently co-authored a monograph titled Spatial Diffusion. She then applied for the graduate program at UF and received an offer of a UF Presidential Scholarship awarded to the University’s top entering graduate students. Marilyn never drew funds from that award because her graduate program at UF was generously and fully funded by contract grants on DEM from the US Military. Her advancements on the topic of DEM were expedient; but, her passion was Epidemiology, Spatial Diffusion of Disease.

After receiving her Ph.D. she was offered several academic appointments and accepted a position as Assistant Professor at Florida State University. After completion of her third year at FSU, she was offered positions at University of Illinois where she advanced to Clinical Professor of Pathobiology.

At University of Illinois she became a cherished teacher, advisor, and mentor. The comments on her FacebookPage from her former students in the USA, India, and Africa, stand as a testament to the high regard she was held by her students, the university, and her biological family. She was a brilliant student; a wonderful person.

I am honored to have been her Ph.D. advisor and her friend

– Grant Ian Thrall

Marilyn O’Hara’s facebook page is at

A selected list of her publications at