A station on the District Line and Piccadilly Line in Travelcard Zone 3. Original opening 1 July 1879, by the Metropolitan District Railway (MDR, now the District line) as Mill Hill Park until 1910 in which year it was rebuilt.
There was formerly a rail link to South Acton Station.
The Wikipedia page is [1] and TfL page [2].
A Grade II listed building - information here.