TMZ reported that Campbell died unexpectedly last month in her home at Portland, Oregon.
A full autopsy examination has been carried out by the Multnomah County Medical Examiner.
Her cousin Sarah Wessling said Jessica had worked a normal day seeing patients at her practice and had returned home to visit her mother and aunt on the day she died.
Wessling recalled how the actress went inside the bathroom and never came out.
The family still tried to revive her as they waited for the emergency medicine team to arrive.
Witherspoon also expressed her condolences in a tweet: "So heart broken to hear this". Her family did not think it was COVID-19, but an autopsy has not yet been concluded. She had been feeling congested, but did not suspect Coronavirus. Working with Jessica on Election was such a pleasure.
"Our dear Jessica suddenly and unexpectedly passed away, leaving behind her 10-year-old son, Oliver".
In the film, she played Tammy Metzler, the sister of school jock Paul whose girlfriend leaves her to start seeing Paul. Entertainment Hub sends condolences to Jessica Campbell's family, friends, and fans during this hard time.
Her last acting credit was in 2002, before she decided to make a career shift to become a naturopathic physician.
And, according to the same media that have the exclusive information on Jessica, a "GoFundMe" page was created to help with the expenses of the cemetery and to support Jessica's 10-year-old son, Oliver, so quickly Judd Apatow, executive producer of "Freaks and Geeks", donated $ 5,000 to the cause.
The family have confirmed that Jessica has been cremated and they are planning a memorial for her.