Lansing Mayor Billy Blackwell died Saturday, city officials said.
He was 61.
Lansing City Administrator Mike Smith said he doesn't have confirmation about the cause of Blackwell's death.
Blackwell had been at the Lansing Fishing Derby on Saturday when he was transported to the hospital.
Lansing City Council President Gene Kirby will be sworn in as mayor Thursday during the next  council meeting.
"Mayor Blackwell’s untimely passing will be a hurdle our city needs to clear," Kirby said in a news release. "I am hopeful that city staff and I can try our best to fill the void that Billy’s passing has left. He will be truly missed.”
Kirby said Blackwell was honest, hard working and fair.
Kirby will serve out the remaining 2.5 years of Blackwell's term as mayor, Smith said.
Once Kirby takes over mayor, the council will have to appoint someone to serve the remaining 10 months of his council term.
Smith said the vacancy probably will be advertised before it's filled. He said a new council president will also be selected.
Blackwell was elected mayor in 2012. Before becoming mayor, he served as a city council member for eight years.
Smith called Blackwell a "go-getter" who had Lansing's best interests at heart.
Smith said Blackwell had been very open as mayor.
"He wanted everything to be transparent," Smith said. "That's what he ran on."
Blackwell had been working to make the city's budget more transparent, Smith said.
Leavenworth County Commission Chairman Bob Holland said Blackwell was a "great man, very friendly."
"He will be sadly missed," Holland said.
Holland asked for a moment of silence in honor a Blackwell at the beginning of Monday's County Commission meeting.
Blackwell retired from the U.S. Army as a lieutenant colonel in 2001 and was employed as a defense contractor by Engineering Professional Services. He served as the team lead for a Signal (Communications) Support contract and taught at the Command and General Staff College at Fort Leavenworth.
Blackwell served on the Lansing Police Force as a reserve officer from 2000-2003 and on the Lansing Parks and Recreation Advisory Board from 2003-2006.
He has also served on numerous steering and bid committees.
Blackwell is originally from Gaffney, S.C. He is survived by his wife, Paulette, son Billy, Jr., and two grandchildren.
R.L. Leintz Funeral Home is handling funeral arrangements.
Visitation will be from 4-6 p.m. Sunday at the funeral home, 4701 10th Ave. A funeral service will begin at 11 a.m. Monday at the funeral home. Burial with full military honors will follow at Mount Muncie Cemetery.
Visitation and the service are open to the public.