Don's Home Places California Counties Northern/Southern California
There is no definitave like between Northern and Southern California.
See Where Exactly Is Northern California? | NSPR
See also North Central Califronia Counties Map

Northern CaliforniaSouthern California 
Alameda
Alpine
Amador
Butte
Calaveras
Colusa
Contra Costa
Del Norte
El Dorado
Fresno
Glenn
Humboldt
Lake
Lassen

Madera
Marin
Mariposa
Mendocino
Merced
Modoc
Mono
Monterey
Napa
Nevada
Placer
Plumas
Sacramento
San Benito
San Francisco

San Joaquin
San Mateo
Santa Clara
Santa Cruz
Shasta
Sierra
Siskiyou
Solano
Sonoma
Stanislaus
Sutter
Tehama
Trinity
Tuolumne
Yolo
Yuba

Kings
Tulare
Inyo
Imperial
Los Angeles
Orange
Riverside
San Bernardino
San Diego
Santa Barbara
Ventura
Kern
San Luis Obispo

Regions Here are a few of other ways to divide California into Regions.

This map was shown on the redistricting page in 2021, but the districts do not line up with this north south line. See Politics.

Links - Sources:
Where Exactly Is Northern California? | NSPR
California County Map | Maps of World