Costume Designers Guild Award for Excellence in Period Television

The Costume Designers Guild Award for Excellence in Period Costume Design for Television Series was awarded for the first time in 2000, honoring 1999 television. While it did honor period costumes, it also honored fantasy television, and the award was titled Costume Designers Guild Award for Excellence in Period/Fantasy Television Series. Those two genres were separated into their own awards categories in 2016, resulting in the current award designation. 
Winners.
1990s.
Excellence in Period/Fantasy for Television
2010s.
Excellence in Period Television