Call this the Case of the Missing Mailboxes.

Early last month, more than 128 mail collection boxes across the city disappeared practically overnight along a curious route extending exactly 26.2 miles.

OK, so that part of it isn’t really much of a mystery.

The mailboxes were removed as a security precaution in advance of the Chicago Marathon, held on Oct. 8, as they have been every year since the Boston Marathon bombing in 2013.

The real head-scratcher is why they haven’t been returned.

OPINION

A process that normally takes days is coming up fast on the one-month mark with no firm promise of a completion date.

Tim Norman, Chicago spokesman for the U.S. Postal Service, confirmed Thursday that only 14 of the mailboxes have been replaced so far.

But he assured me postal employees were working “very quickly” to complete the job, which he described as a “huge task.”

For those Chicagoans who still actually use the mail service, this has become a major irritation.

One of them is a friend of mine. He’s 85 years old. He walks with a cane. The mailbox he normally uses is half a block away from his Old Town home. He’s cool with that.

But it’s a different story when the Postal Service removes all the mailboxes within walking distance and leaves him to take a bus to the nearest post office. That makes him angry.

And you know what Chicagoans do when they get angry: They call their aldermen to complain. And thank god for this, some of them also still contact the newspaper.

Ald. Brian Hopkins (2nd), whose ward is crossed by the marathon route for several miles both out and back, said his office has fielded many of those complaints.

He said it’s been a particular sore spot for residents of the Americana Towers, who rely on a now missing mailbox at Wells Street and North Avenue.

“There’s a lot of senior citizens in that building. It’s a high volume mailbox on a busy intersection. We’ve been calling the post office on a regular basis,” Hopkins said.

Ald. Jason Ervin (28th) said he has received complaints from constituents in the Little Italy neighborhood.

“Some people need the post office,” said Ervin, who called the missing mailboxes a serious problem.

Hopkins said he completely understands the security purpose in temporarily removing the mailboxes. So do I. They’re an easy place to hide a bomb at a busy location.

What he can’t understand is why it’s taking so much longer than normal to put them back. He said he hasn’t received a reason for the delay, but was told the target date for completing the work is Nov. 22.

“Perhaps they put Newman in charge of it,” the alderman joked in reference to the mail carrier character in “Seinfeld.”

Norman, the Postal Service spokesman, made no mention to me of Newman or the Nov. 22 completion date.

Norman explained that it’s much more difficult to replace the mailboxes than to remove them because each box needs to be bolted into the concrete or pavement.

In addition, each mailbox must be returned to the exact location from which it came, because it has a specific coding, he said.

Plus, the Postal Service performs routine maintenance on the boxes before returning them, which can include repairing or replacing locks, he said.

But Norman, a Postal Service veteran in his first year in Chicago, also seemed perplexed by the delay.

“We do apologize for any inconvenience the customers have experienced with this,” he said. “They’re trying to do their best to get these back out there as quickly as possible.”

Sayeth Ald. Hopkins: “Newman!!!!”