Many Tusken raiders died to bring you this information.
Enraged by his mother's death, Anakin had slain an entire camp of Tusken raiders, including women, children...possibly even their animals.
This went down in Attack of the Clones , prior to his fight with Dooku.
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One time Anakin blew up a droid control ship with people on it in orbit around Naboo.
This happened in Star Wars:
Episode I - The Phantom Menace , during the Battle of Naboo.
This was while he was nine, so his earliest kills on record in my opinion.
This ship contained at least 10 non-droids as per this tech guide for Episode One.
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Yes he had (Note: this is a compilation of all answers found thus far plus some more research on my part - consider upvoting the other answers for this question as well)
Here's a list: A gorgoodon (a non-sentient creature, but I thought I'd mention it):
Jedi Quest: Path to Truth Krayn the slave trader (when he was 13)
(Source: Anakin on Wookieepedia )
(note: NOT canon)
The persons on the ship he destroyed in
The Phantom Menace (kudos to Himarm)
The Tusken Raiders following the death of his mother in Episode II (kudos to Praxis - although I did know that one myself!)
Tal Merrik in the series
The Clone Wars (kudos to Null) Genosian Warriors in
The Clone Wars (kudos to Nu'Daq) Saato in Star Wars: The New Droid Army (a video game, I know, but just thought I'd add that one in too) Trenox
(again Star Wars: The New Droid Army ) Messo
(Legends)
Denturi (Anakin's Wookieepedia page cites that he had killed this person, but I can't find much more about Denturi other than that) Durge (was killed by being 'force-pushed' into a star - what a way to die!)
(kudos to Matemáticos Chibchas)
scifi.stackexchange.com/users/22917/Often Right
Yes
As a canon example of Anakin killing a human by lightsaber prior to his execution of Dooku, Anakin killed Tal Merrik .
This image is from
The Clone Wars S02E13 "Voyage of Temptation" .
scifi.stackexchange.com/users/31936/Null
Also, in the foundry scene in Attack of the Clones , he sliced up some Geonosian warriors.
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Was Count Dooku his first kill or had he already slain many a foe?
Had Anakin Skywalker killed anyone before Dooku?
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<star-wars><anakin-skywalker>
scifi.stackexchange.com/questions/92707
scifi.stackexchange.com/users/36812/Josh Schwarzzeskywalker
Prior to Dooku, Anakin had already killed a camp of Tusken Raiders, Tal Merrik, some Geonosian warriors and he also blew up a ship with people on board. It is known Anakin kills an entire camp of Tusken raiders after his mother’s death and that he murders Tal Merrik before he executes Dooku. 
Anakin kills an entire Tusken Raiders’ camp following the death of his mother. Anakin blows up a droid control ship full of people. Anakin slices up some Geonosian warriors. Anakin kills Tal Merrik before he executes Dooku.