Is Fresno in North or South California?

Central California, out in then San Joaquin Valley.

Fresno is central california.

There is no boundary officially defined between North and South California; by most definitions, Fresno is in Northern California.

When we talk of Northern and Southern California, we're talking about coastal metro areas--San Francisco is North (even though it's about in the middle) and LA/San Diego are the South.

Fresno is in the Central Valley, which is about 500 miles from north to south.  Redding, Sacramento, Fresno, Visalia, are all The Central Valley, so they're neither Northern or Southern.

But if you're measuring, Fresno is about the same latitude as Santa Cruz, so it would be Northern California.  (Meaning about the middle.)