While he was a deputy for the sheriff's department, he encountered several supernatural predicaments but didn't believe in it. They ranged from encountering Ennis, questioning Chris Argent about a body, and finding a mutilated Julia Baccari.
His wife, Claudia, was sick with frontotemporal dementia which deteriorated her mental state.
While at the scene of a wreck, a woman who was critically injured told Stilinski that if he wanted to see his wife, he needed to go now. Instead, he stayed with the dying woman. He arrived at the hospital to find his wife died just before he got there. He'd lost the chance to say goodbye. (Alpha Pact)
Only after his son becomes involved with the supernatural and tries to explain it to him did finally start to believe in it. Since then, he has been a pivotal, and at times reluctant, ally of Scott's Pack.
Primary Article - Sheriff Stilinski