Booker's official mayoral schedule in that time included two days with events open to the media and announced in advance.
His last public event was an appearance Thursday at a Congressional Black Caucus conference in Washington.
His recent absence has come as Booker has focused on raising money. He swung through California the last several days, visiting San Francisco on Friday, when another high-profile rally in his name was planned in New Jersey (but then canceled due to outside events).
He went to Hollywood on Monday, where stars Matt Damon and Ben Affleck were listed as hosts at a soiree with donations of $1,000 to $10,000 per person, according to the Hollywood Reporter.
Booker, who has a huge fund-raising lead, also has gone to Washington at least twice in September to meet with top Democratic senators and aides.
"It could seem like voters are being taken for granted," said Patrick Murray, director of the Monmouth University polling institute. "And New Jersey voters do not like to be taken for granted."
Booker, though, also is avoiding pitfalls in a race he is expected to win. He holds huge advantages in name recognition and popularity over Republican Steve Lonegan, and a Stockton Polling Institute survey out Monday gave Booker a 26-point lead.
But a Quinnipiac University poll due out Tuesday is expected to show a tightening race.
"Steve Lonegan is out there on the attack, and the attacks are going unanswered," Murray said.
Quinnipiac poll director Maurice Carroll said his latest poll shows that "it looks like a Booker win, but not the blowout everybody's been looking for."
For the last week, Booker's official campaign schedule has read, "The mayor has no public campaign events today."
Lonegan, by contrast, held seven public events in four counties this past weekend. Lonegan currently holds no public office, while Booker is campaigning while also leading New Jersey's largest city.
His campaign pointed to the need to balance his public appearances with fund-raising, given that he had a short run-up to the unexpected special election and that the winner will also have to run again next year.
"In the 14 days between Labor Day and [Sept. 16], when the mayor left for a fund-raising swing, Cory Booker has attended at least 19 different public events, not including appearances on local news programs," Booker campaign spokesman Kevin Griffis said.
He pointed to stops at a Rutgers University tailgate, a round table discussion with voters, and a public endorsement from Planned Parenthood, among others.
Many of the events Griffis cited, though, were not publicly announced, limiting the scrutiny Booker faced. Some were open only to select media.
Booker attended two public events on Labor Day. Since then he has had only seven publicly advertised campaign events. Four were concentrated on two days, Sept. 14 and 15, leaving three in the 19 other days since Labor Day.
His only other publicly announced events were part of his mayoral schedule: the conference in Washington and a 9/11 memorial in Newark, a setting where political questions are typically put aside.
Several unannounced public appearances, such as a stop at a city school and a backpack giveaway, were part of Booker's work as mayor and had little connection to a statewide campaign. One night he attended a March on Washington event at the Apollo Theater.
Booker's limited appearances have come as questions have swirled about some of his heroic stories and his stewardship of a dilapidated Newark building he once owned. He had no public appearances for two days after releasing his tax returns and announcing that he would sell his shares in an Internet start-up criticized by his opponents.
Griffis, Booker's spokesman, said the mayor is facing "an unprecedented election" in one of America's most expensive media markets.
"To have the resources necessary to communicate your message, you have to throw out the usual rule book and schedule," he said. "Cory Booker is working long hours to earn every vote he can, and the campaign is confident that it has a schedule that will allow him to effectively communicate his message and speak directly with as many New Jerseyans as possible."
Booker had $4.1 million of campaign cash on hand as of July 24, his last report, though some of it can be used only in next year's race.
Lonegan had $151,000 as of his last report. He accused Booker of ducking questions about unemployment and crime in Newark.
"He's failed them as a mayor and the more he's out in public, the more he has to explain this," Lonegan said.
On Friday, as Booker raised money in San Francisco, Lonegan went to Jersey City to rail about Booker's record on crime.
On Monday, as Booker stopped in Hollywood, Lonegan held a fund-raiser in Newark.
"I'm campaigning hard across the state of New Jersey because I respect the voters of this state," Lonegan said. "Cory Booker's parading around San Francisco and Hollywood because, if elected, he'll be representing Hollywood."
On Tuesday Lonegan will appear at Rider University. He is expected to take questions for around 30 minutes.