The museum is usually closed during winter months.
"We know there are going to be a lot of families with relatives coming into town," St. Joseph Museums Jim Hodges said.
The mansion was built in the 1870s for businessman William Wyeth.
He only lived in the house for 10 years.
It has become a popular tourist destination.
"We get people from everywhere, not just Kansas City and Northwest Missouri," Hodges said.
The museum features animal exhibits and a history of St. Joseph and the old west.
In recent years, the mansion has been a popular place for weddings and parties.
The museum will be open until 4 p.m. on Saturday.