By the end of the 1900s, farmers had planted over 500,000 fruit and nut trees in the county, especially plums and pears.
This helped to soften the blows to the agricultural economy caused by the phylloxera infestation in the county's vineyards and upcoming prohibition that crippled the wine industry, but resulted in a boom for shipping grapes to immigrant, home winemakers across the country.

During World War II, the Basalt Rock Company located south of the City of Napa on the Napa River, built 3 dozen salvage rescue tugs for the United States Navy.
Following the war, several small and medium size businesses began operating in the County.
A large majority of these businesses were related to the wine industry and tourism.
Agriculture in the county remained very diverse until late in the 20th century when wine grapes again became the primary focus.
While vineyards were planted on well over 90% of the agricultural land in the county, by the end of the 20th century, modern day farmers have recently begun exploring the possibility of raising other food crops in order to again diversify and take advantage of growing conditions.

At 3:20 a.m. on August 24, 2014, the area was struck by a magnitude 6.0 earthquake centered 3.7 miles (6.0 km) northwest of the city of American Canyon.

In October 2017, parts of the county were affected by wildfires.

From June to July 2018, the County Fire affected a small part of Napa County after crossing over from Yolo County, California.

In October 2019, heavy smoke and unscheduled black outs by Pacific Gas and Electric Company of up to 20,000 customers affected the county due to fierce winds and threats from the Kincade Fire.
By the end of the 1900s, farmers had planted over 500,000 fruit and nut trees in the county, especially plums and pears. This helped to soften the blows to the agricultural economy caused by the phylloxera infestation in the county's vineyards and upcoming prohibition that crippled the wine industry, but resulted in a boom for shipping grapes to immigrant, home winemakers across the country.
During World War II, the Basalt Rock Company located south of the City of Napa on the Napa River, built 3 dozen salvage rescue tugs for the United States Navy. Following the war, several small and medium size businesses began operating in the County. A large majority of these businesses were related to the wine industry and tourism. Agriculture in the county remained very diverse until late in the 20th century when wine grapes again became the primary focus. While vineyards were planted on well over 90% of the agricultural land in the county, by the end of the 20th century, modern day farmers have recently begun exploring the possibility of raising other food crops in order to again diversify and take advantage of growing conditions.
At 3:20 a.m. on August 24, 2014, the area was struck by a magnitude 6.0 earthquake centered 3.7 miles (6.0 km) northwest of the city of American Canyon.
In October 2017, parts of the county were affected by wildfires.
From June to July 2018, the County Fire affected a small part of Napa County after crossing over from Yolo County, California.
In October 2019, heavy smoke and unscheduled black outs by Pacific Gas and Electric Company of up to 20,000 customers affected the county due to fierce winds and threats from the Kincade Fire.
Napa County, California