Short answers, pulled from the story.
Aargau means "Aare province," derived from the Aare River that runs through the region. The reconstructed Old High German form is Argowe, first recorded in writing in 795 in the spelling Argue.
The canton was formed in 1803 under the Act of Mediation, combining three short-lived cantons of the Helvetic Republic: Aargau (1798-1803), Baden (1798-1803), and Fricktal (1802-1803). The canton celebrated its 200th anniversary in 2003.
The Swiss Confederation conquered Aargau in 1415, using Emperor Sigismund's Imperial ban against Frederick IV of Habsburg as a pretext. Habsburg Castle itself was taken by Bern in April 1415.
By 1774, Jews in Aargau were restricted to just two towns, Endingen and Lengnau. They could not own land, could not live under the same roof as Christians, and were required to renew a letter of protection from the governor every sixteen years. Full federal citizenship was granted in July 1863, with residents of Endingen and Lengnau receiving citizens' rights by Grand Council resolution on the 15th of May 1877.
Three of Switzerland's five nuclear power plants are in Aargau: Beznau I, Beznau II, and Leibstadt. Combined with numerous hydroelectric plants on the canton's rivers, this has earned Aargau the informal designation of the energy canton.
The Freie Ämter, or free bailiwicks, were territories around Mellingen, Muri, Villmergen, and Bremgarten governed collectively by the Swiss Confederation. After the Second War of Villmergen in 1712, the fourth Peace of Aarau divided the Freie Ämter along a line running from the gallows in Fahrwangen to the church steeple in Oberlunkhofen, splitting them between different governing cantons.