The question is, what do you define 'in service' as.
The Constitution, while crewed and commissioned, is basically a floating historical object and museum. (and a wonderful place to visit if you get the chance)
The Constellation (
http://www.constellation.org) Commissioned in 1855, was a relief flagship of Battleship Division Five in WW2. This was not a ceremonial duty. She was used so the assigned flagship, the USS Agustia, could be tasked with ship of the line duties.
There were many private vessels pressed into service for local and coastal duties. These were commissioned as "IX Unclassified" for the duration.
The CHRISTINA (IX 80) built in 1892 as a lighthouse tender, she was pressed into service as a seaplane tender during the war.