The price of bitcoin may be on the decline, but that hasn't stopped bitcoin startups from attracting significant funding.

Blockchain, the most popular Bitcoin wallet service, announced Tuesday that it has raised $30.5 million in a Series A round, marking one of the largest funding rounds of any bitcoin startup to date.

See also: These Startups Are Betting Everything on Bitcoin

The bitcoin startup was founded three years ago, but had never taken outside investment. Even so, it managed to build up a user base of more than 2 million wallets.

"As we thought about the next five years for our users and for the company, we knew it was time to bring on additional resources," Blockchain's three cofounders wrote in a blog post announcing the funding. "We searched long and hard for the right investors to bring onto the team to help us scale, to advise us and work with us to bring bitcoin to the next 20 million people."

The funding was led by Lightspeed Venture Partners and Wicklow Capital.

The Blockchain iPhone app

Blockchain was part of the early wave of bitcoin startups that launched before the virtual currency gained mainstream attention and were forced to bootstrap for years. Now investors are increasingly betting on startups in the space: Circle has raised more than $25 million, and Coinbase and BitPay have each raised more than $30 million.

The Blockchain funding comes on the heels of a long slump in bitcoin prices. Bitcoin prices peaked at more than $1,100 late last year, but earlier this month fell below the $300 mark.

Bitcoin prices slumped to an 11-month low over the weekend. Image: Blockchain.info