Casey's campaign reported a little over $6.2 million by Sunday's deadline. Smith's campaign reported almost $2.3 million, most of it his own money.
Casey, the former state auditor general and treasurer from Scranton, is seeking re-election to a second, six-year term.
Smith won a five-way Republican primary on April 24 for the right to challenge Casey. The Armstrong County resident made a small fortune after starting a coal company, and is using it to help bankroll his campaign.
Smith reported spending more than $5.6 million so far, most of it on TV ads in the primary.
The general election is Nov. 6.