The first major U.S. city to host a marathon since the Boston bombings is implementing the tightest security in its race's history.

Bank of America Chicago Marathon organizers and city of Chicago officials confirmed security changes for the Oct. 13 race, which annually draws 45,000 participants and 1.7 million spectators.

This year, the race's start and finish line areas will be locked down to anyone without proper credentials or event-issued bib numbers. Similar to past years, general spectators also won't have access to these areas, marathon organizers said.

"A lot of these policies were in place already," Carey Pinkowski, executive race director of the Bank of America Chicago Marathon, told NBC 5 Chicago. "What we've done is enhance them."

Everyone entering Grant Park, where the race begins and ends, must pass through four designated security and bag screening checkpoints off Michigan Avenue.

Spectators are urged to support runners from other parts of the course, where random bag checks also will take place. Friends and family can meet runners after 9 a.m. at the designated Runner Reunite Area in Grant Park’s Butler Field.

Runners can only bring a clear, plastic event-issued participant bag with them into the park on race day. Organizers said the participant bag is the only one that will be accepted at designated Gear Check tents.

Participants also are advised to wear their event-issued bib number as they enter Grant Park, and spectators "are strongly discouraged" from carrying bags.

“Chicago has a strong record of successfully and safely hosting large-scale events that attract hundreds of thousands of people,” Gary Schenkel, executive director of the Office and Emergency Management and Communication, said. “We are working with race organizers and City departments to implement common sense measures that ensure a safe event for participants, spectators and businesses along the route.”

Another change this year, runners must pick up their own Participant Packets at the Health & Fitness Expo and can no longer pick up packets on behalf of others.

"For our organization and staff and the people involved in the Bank of America Chicago Marathon, the Boston Marathon will be in our consciousness, in our hearts, top of mind," Pinkowski said, "but we have absolute and complete confidence in the city of Chicago, the Chicago Police Department, the city agencies that play such an important role to produce and deliver a safe, secure and memorable race day."

City officials and marathon organizers said they are beginning outreach efforts to race participants, volunteers and fans from around the world to inform the public about these updates.