"Based upon what she was wearing, we believe it is her," Officer Darin Snapp said.
Police said they have a person in custody, but no charges have been filed yet.
Willoughby was last seen with the father of her children Sunday morning and police are questioning him. Her family said she was with her two children, ages 1 and 3.
"Everybody's been talking about the father of her two sons, but he's in custody on something completely separate. But we will definitely be talking to him, though," Snapp said.
Willoughby's family said her children's father told them that she left the children and went with someone else in another car.
"Essence does not leave her children, even while they were at daycare. She's always calling to make sure they are OK," a family friend, Terri Harrison, said.
Police made contact with the 42-year-old father of her two boys, who has a domestic violence history. The young boys are currently staying with their maternal grandparents.
Police received a ping from a cell phone, possibly belonging to Willoughby, near Interstate 435 and Truman Road and were in the area Tuesday morning investigating.
Up until the find Tuesday there was no sign of the mother, and it was the account of her 3-year-old that had police worried about the woman's safety.
Her boys were dropped off by their father's family members, and the older one had a disturbing description of when he last saw her. Police aren't releasing the details about what the toddler said to family members, but said it really helped give them information about what happened.
"We don't know where she is. The only witness, unfortunately, is her 3-year-old son," Harrison said earlier in the day Tuesday.
"I talked to her on Friday, and she was expressing some concerns about him (the father of her children) then being angry," the missing woman's grandfather, Jesse Frazier, said.
Since authorities said Monday they didn't have enough information to assign a whole squad, the young mother's family and friend spent the day passing out fliers and phone numbers in a frantic search of information that could help police take the next step.
They went door-to-door in places that made sense, stopped people on the street and flagged passing cars.
The effort yielded some useful leads for police to follow, including a car and an address where the boys' father was seen just 12 hours before the search party's arrival.
"People are opening up their doors. They are saying they recognize this girl from the neighborhood, so we are hopeful," Vonda Jackson said.
"We hope that Essence will come home and that she will be fine," Harrison said Monday.
Witnesses told police they saw Willoughby near the wooded area at 38th and Topping and their search of the area lead to the gruesome discovery.
Anyone with information to is asked to call the TIPS Hotline at 816-474-TIPS.
Copyright 2012 KCTV (Meredith Corp.) All rights reserved.
Family: Body found at 38th and Topping is that of missing momSearch for missing mother turns into homicide investigationThose who wish to make contributions to help raise funds for the family and childrenMore>>
Thursday, April 24 2014 10:43 PM EDT2014-04-25 02:43:58 GMT
A Marion County waste-to-power plant was reportedly converting medical waste, including human tissue and possibly aborted fetuses, into power.That report prompted Marion County commissioners to scheduleMore >
A Marion County waste-to-power plant was reportedly converting medical waste, including human tissue and possibly aborted fetuses, into power.More >
Wednesday, April 23 2014 3:55 PM EDT2014-04-23 19:55:55 GMT
Two Roseburg parents who took their 2-year-old to the emergency room because she was acting abnormally have been arrested after tests showed methamphetamine in her system. Sheriff's Office spokesmanMore >
Two Roseburg parents who took their 2-year-old to the emergency room because she was acting abnormally have been arrested after tests showed methamphetamine in her system.More >
Wednesday, April 23 2014 5:32 PM EDT2014-04-23 21:32:57 GMT
Two days after a Forest Grove couple found a scrapbook full of old photos in a laundry room wall, FOX 12 viewers helped track down the scrapbook's owner hundreds of miles away. Avamarie Cowles said sheMore >
Mystery solved: A scrapbook found in a laundry room wall at a Forest Grove home belongs to a 76-year-old woman who lives 260 miles away.More >
Wednesday, April 23 2014 8:11 PM EDT2014-04-24 00:11:21 GMT
A man and his girlfriend are on the run after deputies said he crashed a stolen car and she helped him get away. Marion County deputies were called to the 4500 block of Harlan Drive Northeast in SalemMore >
A man and his girlfriend are on the run after deputies said he crashed a stolen car in a Salem neighborhood and she helped him get away.More >
Wednesday, April 23 2014 12:09 PM EDT2014-04-23 16:09:27 GMT
A former UFC fighter who ran a jiu-jitsu academy in Clackamas and served prison time for attempted sex abuse of an underage girl has been deported to Brazil by immigration officials. Hermes Franca De Barros,More >
A former UFC fighter who ran a jiu-jitsu academy in Clackamas and served prison time for attempted sex abuse of an underage girl has been deported to Brazil by immigration officialsMore >
Thursday, April 24 2014 4:40 PM EDT2014-04-24 20:40:50 GMT
Methamphetamine is now the leading cause of illegal drug-related deaths in Oregon. Oregon State Medical Examiner Dr. Karen Gunson released statistics Thursday showing 222 people died in connection toMore >
The Oregon State Medical Examiner released statistics showing 222 people died in connection to the use of heroin, cocaine, methamphetamine or a combination of those drugs in 2013.More >