The Palace of the Governors.
pentagon
The pentagon
It is in New Mexico. The building, called the Hall of Governors, is in the capital city of Santa Fe.
The pentagon.
It is believed to be a fort in Florida that was built by the Spainyards in the 1500s. Now it is just ruins but can be visited in Florida.
There are many thousands of government buildings in the US. The seat of the Federal government is in Washington DC.
Fort Sumter
I don't know ask some one else
The US does not and never has had a new government name
Appalachian Mountains (oldest in US)
The capitol building is the meeting place of the US Congress which is the legislative branch of the US government.
The oldest standing buildings in the US are the Ancestral Puebloan communities found in New Mexico, Arizona, Colorado and Utah. These buildings were built in 750 CE.