It happened at Pinewood Avenue in Woodburn. The man is understood to be a high-profile loyalist.
The ambulance service received a call about 14:15 GMT following reports of a man with a gunshot wound.
After treatment at the scene by paramedics, he was taken to the Royal Victoria Hospital in Belfast.
In the aftermath of the attack, armed police wearing protective masks carried out raids on property in the area.
There has been an ongoing feud between loyalist factions in Carrickfergus for some time.
It is understood one line of enquiry is that the shooting could be connected.
PSNI Supt Darrin Jones said that while the investigation was "still at an early stage police are following significant lines of enquiry".
"Firearms being discharged in a residential area, particularly during daylight hours when children are in the vicinity, is concerning," he added.
"We need the community to give us the information needed so we can remove the dangerous individuals who carried out this attack from our streets and put them before a court of law.
"There will be a continued police presence in the area as we search for those who carried out this brutal attack."
Alliance MLA for East Antrim Stewart Dickson said a "shooting is a very violent incident and it will undoubtedly have caused a great deal of fear and concern".
Ulster Unionist MLA John Stewart said he was "shocked" to hear of the attack and that there was "no justification for such actions".
Detectives are appealing for anyone with information to contact them on 101 or Crimestoppers anonymously by telephoning 0800 555 111.

Some 7.2 million people tuned in to the three-hour show, hosted by How I Met Your Mother star Neil Patrick Harris.
The telecast came second to an NBA finals game between San Antonio and Miami, watched by 11.6 million.
Kinky Boots dominated the awards, winning best musical as well as five other prizes.
Harris, who made his fourth appearance fronting the event, again drew plaudits for his hosting duties and show-stopping opening number.
"It took Neil Patrick Harris only about three minutes to banish any worries that the fearsome Host Fatigue Syndrome would overtake him and the Tony Awards on Sunday night," said the New York Times.
"He set the bar so high with his introductory flourish that fears of another familiar Tony malady haunted the rest of the CBS broadcast: the dreaded How Do We Top the Opening Number Disease."
The Los Angeles Times also praised the "invaluable, unshakeable" Harris.
The 39-year-old, its critic wrote, "was never too long out of view, and when he was around, he was put to good use".
The event also featured appearances from Tom Hanks, Jake Gyllenhaal, Scarlett Johansson, Sally Field and Mike Tyson.
Last year's Tonys was watched by six million viewers, down from the 6.9 million who saw the show in 2011.

Police say it was a suicide attack on a foreign military convoy which was travelling through the area.
A health ministry official said nine Afghans were among the dead.
A senior Nato official confirmed that three American contractors had been killed in the attack in the Macrorayan district.
No group has said it carried out the attack, although in recent months Kabul has been regularly targeted by the Taliban in a series of bombings.
The explosion took place not far from Kabul airport and the presidential palace. Witnesses said that children were among the injured and some foreigners were trapped in a destroyed vehicle.
An interior ministry spokesman quoted by the AP news agency said the blast destroyed more than a dozen civilian vehicles.
The bombing, close to a civilian hospital, is the latest in a series of recent deadly attacks following the announcement of a new Taliban leader.
Earlier this month, a Taliban suicide bomber attacked a checkpoint near the entrance to the international airport in Kabul, killing five people.
Before that, there were three deadly attacks in the city - on a police academy, a Nato base and an Afghan army base that killed at least 50 people.
The Taliban has stepped up its campaign of violence in recent months, taking advantage of the warmer weather of spring and summer. It has made some military gains, especially in northern Afghanistan.
A man in his 40s has been taken to hospital with life-threatening injuries after being shot in the neck in Carrickfergus, County Antrim.
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This year's Tony Awards scored its best US TV ratings since 2009, with viewership up 20% from last year's show, according to the CBS network.
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An explosion has rocked the diplomatic area of the Afghan capital, Kabul, police have said, with at least 12 people killed and 60 injured.