The UKIP leader failed to win the seat, losing out to Conservative candidate Craig Mackinlay.
Mr Farage secured 16,026 votes, with Mr Mackinlay achieving 18,838.
A spokeswoman for Kent Police said "inquires were ongoing" and the force could not say any more at this stage.
The result was not declared at the count at Margate's Winter Gardens until about 10.35 GMT on Friday, hours later than expected.
BBC reporters were told by officials at the time the delays were caused by the sheer volume of ballot papers and problems verifying the postal vote.
Turnout was 69%, up from 65% in 2010.
Claims of suspicious behaviour appeared on social media following the delays.
Labour's South Thanet candidate Will Scobie, who received 11,740 votes, said he thought the count took a long time because they were "trying to do two constituencies at once".
"If police are investigating we'll have to wait and see what the outcome is," he added.
The Thanet South seat was also contested by Ian Driver of the Green Party, who got 1,076 votes, and Liberal Democrat Russell Timpson who secured 932 votes.
Both Mr Driver and Mr Timpson lost their deposits after failing to secure 5% of the vote.
Comedian Al Murray, who stood for election in the guise of The Pub Landlord for the Free United Kingdom Party, came in sixth place with 318 votes.
Mr Farage announced his resignation after failing to become an MP but this was rejected by his party and he continues to be UKIP leader.
Kent Police are making inquiries into a report of electoral fraud in the Thanet South seat, contested in the general election by Nigel Farage.