Era
Ordovician
35
Mississippian
16
1809-1865
10
Pennsylvanian
9
Civil War, 1861-1865
7
Devonian
5
To 1792
5
1734-1820
4
20th century
3
Silurian
3
1906-1984
2
19th century
2
Cambrian
2
Pleistocene
2
Quaternary
2
1743-1826
1
1774-1844
1
1777-1852
1
1792-1865
1
1815-1854
1
18th century
1
1900-1986
1
1905-1989
1
1906-1997
1
1909-1994
1
1924-2015
1
1929
1
1979
1
Carboniferous
1
Colonial period, ca. 1600-1775
1
Cretaceous
1
Eocene
1
Paleozoic
1
Tertiary
1
To 1795
1