You will also see the numbering system used on this page in A Minimalist Catalog of 19th Century United States Stamps.

1847 Issues

1851-1861 Series

1861-1866 Series

1869 Pictorials

1870-1883 Large Bank Note Series

1887-1888 Large Bank Note Series

1890-1893 Small Bank Note Series

1893 Columbian Exposition

1894-1895 First Bureaus

1898 First Bureaus (Changed Colors)

1898 Trans-Mississippi Exposition