Many historical sites remain to mark the birth of this important region in California's formative years.

The Old 5 Mile House stagecoach stop, built in 1890, also operates to this day as a provider of hospitality spanning three centuries.

The Pelton wheel, designed to power gold mines, still drives hydroelectric generators today.

Nevada City and Grass Valley were among the first California towns with electric lights.

(Builder-owner John Flint Kidder's reputation made it clear that he would personally hunt down and kill anyone who tried.)

In Grass Valley, the historic Holbrooke Hotel opened in 1851 and housed Mark Twain, Bret Harte, and four U.S. Presidents (Ulysses S. Grant, Grover Cleveland, Benjamin Harrison, and James A. Garfield).

In 1988, the 49er Fire was accidentally started near Highway 49 by a homeless local man who was suffering from undiagnosed schizophrenia.

Since the enactment of the statute in which the California State Legislature defined the common boundary between Nevada and Sierra Counties in 1874, no survey was conducted to determine where the straight line segment of the common boundary between the two counties ran.

In particular, the statute, at the time codified as Section 3921 of the California Political Code, at the time stated: ...thence south on said state line (state of Nevada) to the northeast corner of Nevada County, a point east of the source of the South Fork of the Middle Yuba River; thence west to the source of, and down the South Fork of the Middle Yuba River to a point ten miles above the mouth of the latter.Since the line had never been surveyed and the legislature never defined where the "point east of the source of the South Fork of the Middle Yuba River" was, the location of the straight air line between the state line and this point was unknown.

As such, both counties claimed that the point east of the source, which itself was also unknown, was located in different places.

This created a situation where a strip of land averaging 1.22 miles in width and around 31.29 square miles were under dispute, with Sierra County claiming that Nevada County was encroaching on their jurisdiction when attempting to levy property taxes.

It also determined that the source of South Fork of the Middle Yuba River was that of several springs in the Sierra Nevada, contrary to the artificial English Lake, which ceased to exist after the failure of its dam in 1883, which is where the source of said waterway was in the eyes of Nevada County.

Also, numerous understory forbs and wildflowers occur, including the yellow mariposa lily (Calochortus luteus).

In 2012, Obama lost by a narrow margin to Mitt Romney, turning the county red once again, only for Hillary Clinton to win it back in 2016 over Donald Trump.

Joe Biden won the county in 2020 with the largest share of votes for a presidential candidate in recent elections, continuing its Democratic shift.

[45] The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.

Nevada County Air Park is a general-aviation airport located just east of Grass Valley.