The couple, who were first spotted together in New York this spring, have bought a converted warehouse loft overlooking the Manhattan skyline, reported the New York Daily News.
"She is renting it, but he stays there. They've been here for a few months now, and they look right at home," a source said.
The pair have been getting increasingly serious since they first stepped out hand-in-hand in April. The 'How I Met Your Mother' actor has been spotted spending plenty of quality time with Williams' daughter Matilda, who turns 7 this weekend.
Williams, 32, previously resided in a brownstone that she had owned with late boyfriend Heath Ledger in family-friendly Boreum Hill.
The couple had bought the home together for USD 3.6 million in 2005.
