The 2017-18 assessment roll jumped by $15 billion or 7.9 percent to a record $206 billion, the first time the roll has breached the $200 billion mark.
Assessor Mark Church attributed the increase to business expansion in the county, which has prompted new construction, job growth and rising real estate prices.
Church said in a statement that growth in business sectors such as technology, life sciences and housing is laying a strong economic base for the future of the county.
The growth in the roll was consistent throughout the county. Total assessed values increased in all 20 cities and in unincorporated areas such as San Francisco International Airport.
New state-mandated assessment standards increased the assessed value of aircraft at the airport, which helped increased the airport's assessed value.
The greatest area of growth in assessed value last year in percentage terms was in East Palo Alto at 19.75 percent followed by Menlo Park at 10.52 percent and San Carlos at 9.13 percent.
Part of the increase in East Palo Alto was due to the rise in the value of homes.
Officials with the assessor's office called East Palo Alto one of the last affordable places on the Peninsula.
In Menlo Park and other cities nearby, homebuyers have been purchasing older homes and renovating or demolishing them. That also has driven up the assessed roll.
The roll has also increased as home prices have gone up with the demand for homes, according to the assessor's office.
The assessed roll is the value of all properties in the county as of January 1 of each year.
The roll reflects changes in property ownership, new construction, drops in property value and the restoration of values from the previous year.