The Labour leader said he was succeeding in getting people to "take another look" at Labour, and that it was clear the party was making inroads under his leadership.
But he conceded he still faces "a big challenge" in winning back voters across Staffordshire and the Black Country, where the Conservatives won 22 out of 25 seats at the last general election.
He said his British Recovery Bonds scheme could help the region bounce back after the pandemic, with funds coming from it used to create new infrastructure and jobs.
It came as the latest polls show Labour trailing further behind the Tories, with Sir Keir's popularity rating dropping below Boris Johnson's.
Sir Keir was speaking to the Express & Star at the launch of Labour MP Liam Byrne's campaign for West Midlands Mayor.
Asked if he thought his message was getting through to voters in the West Midlands, Sir Keir said: "I think it is, but it's a big challenge that we've got.
"This is a four year exercise and I think people are taking another look at Labour. Have we got a long way to go? You bet we have.
"Winning in the West Midlands in May is an extremely important step in the right direction."
Sir Keir also defended his British Recovery Bonds plan – announced last week – which would see a Labour government offer a savings account similar to National Savings and Investment income bonds.
He said the scheme, which has been criticised over claims it excludes people who have struggled financially during the pandemic, was "one idea amongst many others"
"We hope that billions of pounds will be raised through these bonds," he said. "The money can be used to rebuild the regions and I think it should be used for infrastructure."
Conservative Chair Amanda Milling, the Cannock Chase MP, accused Sir Keir of stealing her party's ideas and offering nothing but "empty rhetoric".