2016 Annual Lane County Homeless Point in Time Count
http://bit.ly/2lR74mc

Of the 1,451 people counted: 
434 people have a mental illness = 30 %
232 people have chronic alcohol/substance abuse issues = 16 %
Total = 666 = 46 %

The total is somewhat misleading because there is probably a lot of overlap between the two categories. Mentally ill people often self-medicate with alcohol or other drugs to feel better. Homelessness is very stressful, making mental illness and drug use worse. Secure shelter helps both. 

Nationally it is recognized that a “shelter first” policy is the best way of helping the chronically homeless – putting them in apartments and paying their rent. Once they’re safely sheltered other help can be offered. It actually saves money that is currently being spent on jails, ER visits, etc.