An earlier mention as de Senegaune, ostensibly dated to 765, survives in a 16th-century copy.

[3] The etymology of the name is unknown; San- seems to have changed to Sar- under the influence of the hydronym Saar.

A popular etymology connecting the name Sargans to "goose" (German Gans) may date to as early as the 15th century.

The town was given limited rights of self-government in 1456 when the count agreed to select a Schultheiss out of a list of three candidates to be submitted by the burghers.

In 1483, count Jürg of Werdenberg-Sargans was forced to sell the county to the Swiss Confederacy for 15,000 Rhenish guilder.

Sargans is at the juncture of the railway lines connecting Chur with Zürich and with Lake Constance, built in 1859.

Sargans remained mostly unaffected by industrialisation; the Gonzen iron ore mine was closed down in 1966.

Of the rest of the land, 20.2% is settled (buildings or roads) and the remainder (6.2%) is non-productive (rivers or lakes).

As it is located at the intersection of the Rhine and Seez valleys, Sargans has long been important in both a strategic and commercial sense.

It consists of the village of Sargans and the hamlets of Vild, Ratell, Prod, Splee, Riet, Farb, Töbeli and Schwefelbad.

Trains heading north toward St. Gallen, east toward Chur and Ticino, and toward Austria, all pass through Sargans.

Of the foreign population, (as of 2000[update]), 34 are from Germany, 126 are from Italy, 432 are from former Yugoslavia, 38 are from Austria, 50 are from Turkey, and 228 are from other countries.

[9] The historical population is given in the following table:[3] From the 2000 census[update], 3,001 or 63.0% are Roman Catholic, while 843 or 17.7% belonged to the Swiss Reformed Church.

[12] Both the local mining operation and Schloss Sargans are listed as Swiss heritage sites of national significance.

The wettest month is August during which time Sargans receives an average of 153 mm (6.0 in) of rain or snow.

The month with the most days of precipitation is June, with an average of 14.5, but with only 136 mm (5.4 in) of rain or snow.