Both the roads and airports are expected to be busy, but if you're flying, there's a warning about bringing marijuana to the airport.
RELATED: Illinois Weed Legalization Guide
While recreational marijuana becomes legal in Illinois on January 1, it is still illegal to possess according to federal law. It's illegal to bring it across state lines and may be illegal in the country you're visiting.
"To ensure safe travel for all residents and visitors, we're encouraging all travelers not to bring cannabis through Chicago's airports as it still remains illegal under federal law," said Chicago Police Commander William Mullane."
TSA and Chicago police said they cannot force you to give up the cannabis if you meet the legal requirements for possession in Illinois.
"If it is not a violation of the statute or ordinance, we would offer them a proper disposal of the cannabis if they wish, or they could continue on with their travels," Commander Mullane said.
Illinois Weed Legalization Guide: Will your city or town sell marijuana?
"Our officers are not looking for any cannabis as they go through their normal security duties," said Louis Traverzo with TSA. "But should they come across it, we are going to contact the Chicago Police Department to make a final determination on the disposition."
Chicago officials expect Friday to be the busiest day of the holiday travel stretch, with 5 million expected to fly through the city's airports.
It is recommended travelers get to the airport two hours early for domestic flights and three hours for international flights.
Already there were happy reunions at baggage claim. Belinda Petroskey met her daughter at the airport, excited to spend the holiday with her in Northwest Indiana.
"She moved to Portland several years ago on her own and decided she misses coming home for Christmas, so she comes home every year," she said.
Shawna Weeks has been away from home for basic training.
"It has been four months since I have seen them, since I started basic, and I am still in training," she said.
Traveling this time of year can be a challenge, so United Airlines' "pawfessionals" will be will be around throughout the weekend to lift spirits. Richard Martin, director of K-9 ministries for Lutheran Church Charities, loves seeing how people respond to the golden retrievers.
"You can see the emotion in their bodies. You can see the stress literally just come out of it just by looking at the dogs," he said.
"I haven't seen a dog in forever," said traveler Kallysta Arnold. "It has been a long time going from basic to AIT [Advanced Individual Training]. I missed my dog so much. They just made it 100 times better."