Schenectady police Lt. Mark McCracken said Robert Butler of Saratoga Springs was arraigned in Schenectady City Court on a first-degree arson charge and was sent to the county jail without bail.
McCracken said Butler was known to the family.
David Terry, 33, was killed along with 3-year-old Layah Terry, 2-year-old Michael Terry, and 11-month-old Donavan Duell. Safyre Terry, 5, was taken to the burn unit at Westchester Medical Center where she was last listed in critical condition.
The Terry children were David Terry's biological children. Jennica Duell, the mother of all four children, was not at home when the fire broke out.
Autopsy results may determine if Butler will face more charges.
The fire in Schenectady, a city of 66,000 just west of the capital of Albany, broke out shortly after 4 a.m. Thursday. Fire Chief Michael Della Rocco said the wood-frame building burned quickly and completely largely because the residence was built in the style of the late 19th- and early 20th-century known as "balloon construction," in which studs run from the ground to the roof without fire-breaks, now required by modern codes.
City fire investigators were working with state and federal agencies to try to determine the cause. Della Rocco said the building will be condemned and demolished.
Police said Butler would be represented by the county public defender's office. A message left with the office was not immediately returned Friday.