It is understood the assault happened at Thomas Russell Park in Downpatrick on Friday afternoon.
She has been living in the property with a young child for some time.
The 30-year-old was arrested last night and taken into custody for questioning.
Chief Inspector Joe McMinn said: “Police are currently investigating the circumstances surrounding an incident at a house in the Downpatrick area.
“A woman has been taken to hospital with serious injuries following the incident.
“Officers are working to establish how the woman sustained her injuries. There are no further details at present.”
SDLP South Down MP Margaret Ritchie said: “I offer my support and prayers to this woman this evening.
“I would also urge anybody with information to contact police.”
Anyone with information is asked to contact police in Downpatrick on the 101 number.