Hillary Clinton is the first woman nominated for President by a major party. This is an important milestone that will only be exceeded by her being elected President. It will rank along side of the election of Barack Obama as the first person of color to be elected President.
Since I don't want to ignore Donald Trump, because we all know how whiny he can get, if Trump is elected he will be the first person with absolutely no prior experience in public service (elected office, cabinet post, victorious general) to be gifted the presidency.
Here are a few other notable firsts:
First Woman Elected To Congress: Jeannette Rankin
First Woman Elected to the Senate: Hattie Caraway
First Women Elected Governors of a State: Miriam Ferguson, Nellie Ross
Then there was "Ma" Ferguson of Texas. In typical Texas fashion, her husband, James "Pa" Ferguson, had been governor when he was impeached and removed from office in 1917. When she ran a common campaign slogan was "Me for Ma, and I Ain't Got a Durned Thing Against Pa." She lost a reelection bid in 1926 mostly because her husband had again got caught with his hands in the public till. She ran and won again in 1932.
First Women Senator Elected on Her Own: Margaret Chase Smith