Virginia State Police cleared Jeff C. McKay, the Democratic chairman-elect of the Fairfax County Board of Supervisors, of allegations that he benefited from a quid pro quo relationship with two developers while buying his family home in 2017.

In a letter to McKay’s lawyer released Tuesday, Deputy Commonwealth’s Attorney Robert McClain said police found “no evidence of criminal culpability” in examining McKay’s home purchase.

McClain said his office therefore would not prosecute the veteran supervisor, who has represented the Lee district since 2008.

“I’m pleased this matter has come to a close. It was never anything more than an unfortunate, baseless, personal attack made for political gain by one of my opponents,” McKay said in a statement. “We have real issues to tackle like transportation, affordable housing and the environment. . . . I can’t wait to continue that work in this new chapter.”

The allegations had dogged McKay since the Democratic primary elections this year.

A memo commissioned by one of his political rivals — developer Timothy M. Chapman — used public records to imply that McKay arranged for a portion of the Kingstowne Towne Center to be rezoned in exchange for a deal on the five-bedroom home in the county’s Alexandria section that he and his wife brought from a developer friend for $850,000.

The memo noted that Warren Halle, whose Halle Cos. owns the Kingstowne development, has been a major contributor to McKay. The memo also said that around the time the 2016 vote on the rezoning was set to occur, Michael A. McGhan, McKay’s developer friend, was in the process of buying land on Roxann Road owned by Halle that eventually would include McKay’s home.

Although sales records showed the $850,000 price was slightly more than the home’s assessed value, the memo contended that it was below fair market value for a house of that size and that nobody else was allowed to bid for the home.

McKay called the allegations, which were initially circulated anonymously, “borderline libelous.” He hired a veteran land-use attorney who investigated the claims and debunked them in a report, calling Chapman’s memo a political “witch hunt.”

Nonetheless, Chapman filed an ethics complaint in May with Virginia State Police that contended the difference between the home’s fair market value and the actual sales price should have been reported as a gift.

The complaint allowed Chapman and other Democrats in the primary to accuse McKay, the front-runner, of being too cozy with developers.

After McKay won that race, Republican Joseph Galdo continued the line of attack, suggesting that developers with easy access to supervisors have been allowed to overbuild in some areas of the county.

McKay met with state police in September, in hopes of putting the allegations behind him before the Nov. 5 election. But the issue remained unresolved on Election Day.

McKay beat Galdo by 33 percentage points to replace outgoing board Chairman Sharon Bulova (D). Starting in January, he will lead a board where Democrats will have a 9-to-1 majority, overseeing governance of Virginia’s most populous and economically powerful jurisdiction.