What a difference two years can make.
Back in the distant past of 2015, the number of potential candidates was so scant, the former head of the city’s Election Department complained of “no action” that year.
But on Wednesday — the day officials began accepting applications for nominating papers for the 2017 municipal elections — there was a flurry of activity at City Hall. Candidates have until May 16 to sign up, and by the end of Wednesday, nearly 40 people had.
Many of the hopefuls are seeking a trio of open councilor seats, and a few candidates pulled papers to run for mayor, which was not on the ballot in 2015.
Candidates must gather scores of signatures from registered voters to make the ballot — 3,000 signatures to run for mayor; 200 for most council districts or 1,500 for an at-large seat. Election officials must verify the signatures. Serious challengers have to raise money and build a campaign, both daunting prospects for those with long odds. The preliminary contest is Sept. 26, and the election is Nov. 7.
Mayor Martin J. Walsh, who has been cruising on national prominence and millions of dollars in campaign cash, had four potential challengers as of Wednesday, elections officials said.
His main challenger is Councilor Tito Jackson, who said in January that he would run on a platform that highlights the city’s growing income divide.
On Wednesday, Walsh urged his Twitter followers to help “build a better Boston for everyone.”
“Today, I filed to run for reelection as your mayor,’’ he tweeted.
Jackson also rallied his supporters and asked for their help in gathering signatures.
“Today I take the first official step to become Boston’s next Mayor. I run because we must be a city for all, not just for some. #WeAreBoston,” Jackson tweeted.
Other lesser-known potential mayoral challengers emerged Wednesday. They are Mary A. Franklin, a vocal public safety advocate from Roslindale; Donald M. Osgood Sr. of Dorchester; and Christopher G. Womack.
In the at-large council race, five challengers got their applications for nomination papers Wednesday in their bid to unseat four incumbents — Michelle Wu, Michael Flaherty, Ayanna Pressley, and Annissa Essaibi-George.
The potential challengers are William A. King, Aziza A. Robinson-Goodnight, and perennial candidate Althea Garrison, all of Dorchester; Domingos DaRosa of Hyde Park; and Robert F. Couture Jr. of the Fenway.
But all eyes are on three open council seats made possible by the departing Jackson, the District 7 councilor; Councilor Salvatore LaMattina of East Boston; and Councilor Bill Linehan of South Boston.
Two City Hall employees are vying so far for LaMattina’s job: Lydia M. Edwards, a 36-year-old East Boston resident, who is deputy director of the Boston Office of Housing Stability; and Jack Kelly III, a 36-year-old Charlestown resident and the addiction and mental health policy adviser for Linehan.
Stephen Passacantilli, a 42-year-old North End resident, said he is officially in the race. He said he is vacationing in the Caribbean this week with his family and did not get the application papers yet.
The other potential candidates are Jack E. Frias and Michael Sinatra, both of East Boston, election officials said.
Edwards, a union activist and lawyer who advocated for the Domestic Workers’ Bill of Rights, announced her candidacy Tuesday.
“I really believe in the power of people being able to get things done,’’ she said.
Passacantilli comes from three generations of local political leaders, was an aide to LaMattina, and served as a staunch campaigner for Walsh in the 2013 mayoral race. Passacantilli is the operations specialist in the city’s Economic Development Department.
“I love my neighborhood, and I love the district that I am going to hopefully represent,” he said.
He and Edwards said they will seek leaves of absence from their city jobs to campaign.
Kelly, who developed an app that connects addicts in recovery to assistance, ran unsuccessfully for an at-large seat in the 2013 election.
In District 2, which includes South Boston, Chinatown, downtown, and the South End, there are seven potential candidates so far. South Boston residents Corey Dinopoulos and Edward M. Flynn and Bay Village resident Michael S. Kelley have previously announced their intentions to run.
The others vying are Joseph F. Kebartas, James M. Lauper, and Erica Tritta, all of South Boston, and Peter Lin-Marcus of Chinatown, election officials said.
In District 7, elections officials said six candidates have signed up: Angelina M. Camacho, Joao Gomes DePina, Kim Janey, Deeqo Jibril, Charles Clemons Muhammad, and Wilson Rodriquez.
Hassan Williams, Rufus Faulk, and former state representative Carlos Henriquez have previously announced they plan on running.Meghan E. Irons can be reached at email@example.com. Follow her on Twitter @meghanirons.