ST. LOUIS (KSDK) – People will notice a lot of activity at post offices across the St. Louis metropolitan area Monday.

The United States Postal Service says it's the busiest mailing day of the year. USPS said more than 607 million pieces of mail will be processed.

More than 3 million pieces will be processed in St Louis area, which is about three times the average daily workload.

USPS officials say it takes extra hours and staffing to make sure everything is delivered in time – but pack your patience before you head to your local post office. Less time until Christmas can mean longer lines and wait times for customers.

In order to make sure your package arrives on time ahead of Christmas, first-class mail must be postmarked by December 20, priority mail must be postmarked by December 21 and the express deadline is December 23.