The 1st Senate District is made up of 11 counties in Northern California and is home to nearly one million people. It covers most of the Sierra Nevada Mountain Range from the Oregon border in Modoc County and travels south along the Nevada border into El Dorado and Alpine Counties. It is made up of all or parts of: Alpine, El Dorado, Lassen, Modoc, Nevada, Placer, Plumas, Sacramento, Shasta, Siskiyou and Sierra counties. It is a diverse district that also includes many of the Sacramento suburbs. Major cities within the district include: Yreka, Redding, Auburn, South Lake Tahoe, Truckee, Grass Valley, Folsom, Placerville, El Dorado Hills, Susanville, Quincy and Alturas.
- Green: Senate District 1 map
- Pink: Additional areas assigned to represent until 2024.