Helen Dann and Francis Marion Dyer were not married yet on the 1900 Census. If they married in 1900, it would have been after the Census. The 1910 Census, however, states they had been married 9 years, so it looks like it could have been 1901 when they wed.
Also, they did not marry in CT. They married in MT, where he had been living for several years, next door to his uncle Bluford Dyer.
I have a long line of genealogy on the Dyer line, and a few notes on the Dann line as well, at my Rootsweb site, per the following link:
I wonder what happened to Helen's grandfather Selleck Dann and grandmother Pedee (Pierce) Dann? Did they separate? He was in a boarding house in Whitewater, Walmouth Co., WI, no family with him, in 1880. I cannot find her Pedee or any of their kids in 1880. (A lot of sources list her as Peder!) But then Pedee and two daughters show up on the 1885 Territorial Census of South Dakota.
Then in 1900, Pedee is in Great Falls, Cascade Co., MT, listed as a widow, although husband Selleck (aka Sellek, aka Sellick) is back in Stamford CT, at his brother Charles Dann's home.